Mainland China, also known as the Chinese mainland, is the geopolitical as well as geographical area under the direct jurisdiction of the People's Republic of China (PRC). It includes Hainan island and strictly speaking, politically, does not include the special administrative regions of Hong Kong and Macau, even though both are partially on the geographic mainland (continental landmass).
In the PRC, the usage of the two terms are strictly speaking not interchangeable. To emphasize "equal footing" in Cross-Strait relations, the term must be used in official contexts with reference to Taiwan, with the PRC referring to itself as "the mainland side" (as opposed to "the Taiwan side"). But in its relations with Hong Kong and Macau, the PRC government refers to itself as "the Central People's Government", and Mainland China excluding Hong Kong and Macau is referred as Nèidì.
In the 1930s the region faced Japanese invasion. By 1949, the Communist Party of China's (CPC) People's Liberation Army had largely defeated the Kuomintang (KMT)'s National Revolutionary Army in the Chinese Civil War on the mainland. This forced the Kuomintang to relocate the Government and institutions of the Republic of China to the relative safety of Taiwan, an island which was placed under the control of the Republic of China after the surrender of Japan at the end of World War II in 1945. With the establishment of the People's Republic of China on October 1, 1949, the CPC-controlled government saw itself as the sole legitimate government of China, competing with the claims of the Republic of China, whose authority is now limited to Taiwan and other islands. This has resulted in a situation in which two co-existing governments compete for international legitimacy and recognition as the "government of China".
The phrase "mainland China" emerged as a politically neutral term to refer to the area under control of the Communist Party of China, and later to the administration of the PRC itself. Until the late 1970s, both the PRC and ROC envisioned a military takeover of the other. During this time the ROC referred to the PRC government as "Communist Bandits" (共匪) while the PRC referred to the ROC as "Chiang Bandits" (蔣匪). Later, as a military solution became less feasible, the ROC referred to the PRC as "Communist China"" (中共). With the democratization of Taiwan in the 1990s, the phrase "mainland China" soon grew to mean not only the area under the control of the Communist Party of China, but also a more neutral means to refer to the People's Republic of China government; this usage remains prevalent by the KMT today.
Due to their status as colonies of foreign states during the establishment of the People's Republic of China in 1949, the phrase "mainland China" excludes Hong Kong and Macau. Since the return of Hong Kong and Macau to Chinese sovereignty in 1997 and 1999, respectively, the two territories have retained their legal, political, and economic systems. The territories also have their distinct identities. Therefore, "mainland China" generally continues to exclude these territories, because of the "One country, two systems" policy adopted by the PRC central government towards the regions. The term is also used in economic indicators, such as the IMD Competitiveness Report. International news media often use "China" to refer only to mainland China or the People's Republic of China.
In the People's Republic of China, the term 内地 ("Inland") is often contrasted with the term 境外 ("outside the border") for things outside the mainland region. Examples include "Administration of Foreign-funded Banks" (中華人民共和國外資銀行管理條例) or the "Measures on Administration of Representative Offices of Foreign Insurance Institutions" (外國保險機構駐華代表機構管理辦法).
Hainan is an offshore island, therefore geographically not part of the continental mainland. Nevertheless, politically it is common practice to consider it part of the mainland because its government, legal and political systems do not differ from the rest of the People's Republic within the geographical mainland. Nonetheless, Hainanese people still refer to the geographic mainland as "the mainland" and call its residents "mainlanders". In some coastal provinces such as Guangdong, Fujian and Jiangsu, people often call the area of non-coastal provinces in of Mainland China as "Inland" (内地).
On July 15, 1947, during which mainland China was governed by the Republic of China, the Document 0744 ordered the Chinese Communist Party and its forces to be called "Communist bandits" as a form of rectification of names, to the exclusion of all other terms, such as "Red bandits"(In Chinese 赤匪).
After the Republic of China's relocation to Taiwan, the Kuomintang party-state imbued the term dalu with nostalgic overtones, associating it with "the land of the utopian past [and] childhood". Schoolchildren were taught slogans like "Counterattack the mainland!" (反攻大陸！) and "Save our mainland compatriots from the deepest water and hottest fire!" (拯救大陸同胞于水深火熱之中！). The Taiwanese were also told that they were the guardians of traditional Chinese culture until political reunification. However, democratization on Taiwan has led to the rise of voices which denounced traditional attitudes towards the mainland and the ancestral home system, pressing for Taiwanization, Desinicization, and "Taiwan cultural independence" (文化台獨). Concurrently, the mainland Chinese economic reform changed the connotation of "mainland China" to one of "primitiveness, nativeness, and raw cultural material for economic gain", as well as condescention because of Taiwan's comparatively advanced economy. Warlike phrases like "Counterattack the mainland!" saw a revival, but in reference to the economic expansion of Taiwanese businesses. Despite the re-branding of the Kuomintang in the 1990s as a party "native" to Taiwan, Kuomintang continues to produce a variety of mainland-related media such as the television program "Searching for the Strange on the Mainland" (大陸尋奇).
In Taiwan, there are differing opinions as to the neutrality of the term "mainland China". However, the term is considered somewhat more neutral than historical terms used to describe the territories under the control of the People's Republic of China (PRC) (which is in turn controlled by the Chinese Communist Party (CCP/CPC)).
Traditionally, the Republic of China on Taiwan (led by the Kuomintang/Nationalists (KMT/GMD)) has referred to the territories under the control of the Chinese Communist Party with several different names, e.g. "(territory controlled by the) Communist bandits", "occupied/unfree area (of China)" (as opposed to the "free area of the Republic of China"), "Communist China" (as opposed to either "Nationalist China" or "Democratic China"), "Red China" (as opposed to "Blue China"), and "mainland China (area)". In modern times, the term "Communist bandits" is generally considered both inflammatory and offensive by supporters of the Kuomintang and other Pan-Blue political parties [the KMT and other aligned parties believe that "China" encompasses both sides of the Taiwan Strait], so it is no longer commonly used by them. Similarly, terms implying illegal occupation (of the mainland) or an intent to reclaim the mainland tend not to be used by both Pan-Blue and Pan-Green individuals. Therefore, only the terms "Communist China" or "mainland China" are still commonly used by Taiwanese (Chinese) people aligned with Pan-Blue ideologies. Somewhat synonymous to the term "Communist China" is the term "People's Republic of China (PRC)" (which is either considered to encompass Hong Kong and Macau or isn't, due to the confusion and ambiguity of One Country Two Systems). Meanwhile, the term "mainland China" is often simply abbreviated to "the mainland" among speakers of Chinese in Taiwan or from Taiwan.
However, the Pan-Green Coalition in Taiwan, led by the Democratic Progressive Party (DPP) [the DPP and other aligned parties usually support Taiwanese independence to a certain degree], tend to be opposed to suggestions that Taiwan is part of China, regardless of the subtlety of said suggestions. Referring to the territories under the control of the Chinese Communist Party as "mainland China" suggests that Taiwan is part of China. That is, the term "mainland China" suggests that Taiwan is a "satellite island" of China, and that Taiwan is tethered to China (much in the same way that one might say that "Kinmen is tethered to Taiwan"). Therefore, Pan-Green individuals tend to prefer the term "China", rather than "mainland China", since the term "China" suggests that Taiwan and China are two separate countries. Pan-Green Taiwanese might also prefer to refer to China as "Communist China" or "the People's Republic of China (PRC)" or "Red China". However, these terms suggest that there exist "two Chinas". Certain Pan-Green Taiwanese believe that there exist "two Chinas" and that the Republic of China (ROC) and Taiwan are one and the same, so they would be more inclined to use these terms (compared to those who believe that the ROC is illegally occupying Taiwan). Individuals in Taiwan who are aligned with Pan-Green ideologies might be more inclined to refer to the People's Republic of China as "the Communist bandits" or "occupied/unfree area" (compared to those aligned with Pan-Blue ideologies), due to their negative (or indifferent) views towards mainland China and the Chinese Communist Party, though they generally don't have any intention of "reclaiming the mainland".
Government organizations and official and legal documents in Taiwan, including the Republic of China (ROC) Constitution, use the term "the mainland" to refer to territory controlled by the PRC (excluding the claimed area of the Free Area). Since the ROC government has never recognized the establishment of the PRC and because the Constitution of the ROC does not allow the existence of another state within its territory, constitutional amendments made in the 1990s had to refer to the area occupied by the PRC as "mainland", since that territory was still officially considered to be part of the ROC's sovereign territory which was just under illegal enemy occupation.
Due to the issue of national identity (i.e. "Chinese versus Taiwanese"), the Democratic Progressive Party and other aligned parties would prefer to amend the ROC constitution to limit its scope and territorial description to the Free area of the Republic of China only and formally change the name of the Republic of China to "Republic of Taiwan" instead, thereby eliminating the need to refer to the "mainland area" and "Free Area" altogether.
In 1992, a high-level political meeting between the ROC and PRC was held in Hong Kong where what became called the "1992 Consensus" developed. This "consensus" essentially reaffirmed that both the ROC (then under KMT administration) and the PRC agree there is only "one China" in a definition that covers both sides of Taiwan Strait, but they differ on their own interpretation of what that "China" means. Each interprets and believes it is the legitimate government of China and has a claim on the territories held by the other. In this context, the term "Mainland China" is agreeable to both sides since they both conceive "China" as including mainland and Taiwan, and therefore need this term to distinguish the two areas. However, since it was the KMT who came to this consensus with mainland China, the Pan Green Coalition does not embrace this term as the Pan Blue Coalition does.
In Taiwan, the term "Waishengren" (外省人; wàishěngrén; 'external province person(s)') is used to describe an ethnic or sub-ethnic group which officially comprises around 14% of the population of Taiwan. Waishengren were originally people who migrated from mainland China to Taiwan immediately after the supposed "Retrocession" of Taiwan to the Republic of China, following the Japanese surrender of 1945. Waishengren are most commonly associated with those Chinese who migrated to Taiwan with the Kuomintang (KMT) around the end of the Chinese Civil War in 1949. However, the term has become somewhat outdated in modern times, as it now refers to the descendants of the original Waishengren, spanning across 74 years of modern history. Most modern Waishengren were born and raised in Taiwan. However, the term still sees usage in Taiwan (e.g. "New Taiwanese", a related term coined by former ROC-president Lee Teng-hui) due to the reality that many children of Waishengren were raised with "Mainland Chinese" family values and national ideologies (and therefore don't often share the same values and identity as "Benshengren" (本省人; běnshěngrén; 'original province person(s)'), or "Native Taiwanese"). The status of Waishengren in Taiwan is a divisive political issue. For many years, certain groups of Waishengren were given special treatment by the KMT government, which had imposed martial law on Taiwan. More recently, pro-Taiwan independence politicians have been calling into question the loyalty and devotion of Waishengren to Taiwan, whereas pro-Chinese reunification politicians have been accusing the pro-independence politicians of playing identity politics.
In modern times, the term "Mainlander" mostly refers to "Daluren" (大陆人; 大陸人; dàlùrén; 'mainland person(s)'), meaning people who live in China (PRC), i.e. mainland China. The term does not generally refer to people living in Hong Kong and Macau, even though those regions are nominally under the sovereignty of the PRC. The term also usually isn't used to refer to residents of Kinmen and Matsu, islands which are under the control of the ROC and are administered as "Streamlined Fujian Province" (i.e. they are not part of Taiwan). However, the islands of Kinmen and Matsu are geographically much closer to "mainland China" than Taiwan and have historically been separate from Taiwan. Kinmenese and Matsunese are commonly referred to by foreign media as "Taiwanese", but they generally prefer to refer to themselves as "Kinmenese" and "Matsunese", respectively (i.e. they neither prefer to be labeled as "Taiwanese" nor "Mainlander", but as something else entirely).
Hong Kong and Macau are both sovereign territories of the People's Republic of China. However, due to the One Country Two Systems policy, the two regions maintain a high degree of autonomy, hence why they are usually considered not to be part of mainland China, similarly to Taiwan.
Geologically speaking, Hong Kong and Macau are both connected to mainland China in certain areas (e.g. the north of the New Territories). Additionally, the islands contained within Hong Kong (e.g. Hong Kong Island) and Macau are much closer to mainland China than Taiwan and Hainan, and are much smaller.
In Hong Kong and Macau, the terms "mainland China" and "mainlander" are frequently used for people from PRC-governed areas (i.e. not Taiwan, Hong Kong, and Macau). The Chinese term Neidi (內地), meaning the inland but still translated mainland in English, is commonly applied by SAR governments to represent non-SAR areas of PRC, including Hainan province and coastal regions of mainland China, such as "Constitutional and Mainland Affairs" (政制及內地事務局) and Immigration Departments. In the (as well as the ) the CPG also uses the Chinese characters 内地 "inner land", with the note that they refer to the "customs territory of China".
In the United States' Taiwan Relations Act, the ROC-controlled islands of Quemoy and Matsu were excluded from the definition of "Taiwan". The House Foreign Affairs Committee justified this exclusion on the grounds that "Quemoy and Matsu are considered by both Taipei and by Beijing to be part of mainland China". Quemoy and Matsu are geologically part of the continental mainland.
Other use of geography-related terms are also often used where neutrality is required.