Strikethrough is a typographical presentation of words with a horizontal line through their center, resulting in text like this. Contrary to censored or sanitized (redacted) texts, the words remain readable. This presentation signifies one of two meanings. In ink-written, typewritten, or other non-erasable text, the words are a mistake and not meant for inclusion. When used on a computer screen, however, it indicates deleted information. It can also be used deliberately to imply a change of thought (as in epanorthosis).

Strikethrough is primarily used to mark text that is mistaken or to be removed. Historically, this has also been marked by placing dots under the letters to be ignored (Latin: punctum delens).[1]

In quantum field theory, a slash through a symbol, such as , is shorthand for γμaμ, where a is a covariant four-vector, the γμ are the gamma matrices, and the repeated index μ is summed over according to the Einstein notation.

In medieval manuscripts such as the Domesday Book, "strikethrough" of text with red ink often functions as highlighting similar to modern underline.[2]

The HTML presentational inline element for strikethrough is <strike> or <s> This element was, however, deprecated in the 1999 HTML 4.01 standard, and replaced by the <del> tag, a semantic element representing deleted text, which user agents (typically web browsers) often render as a strikethrough.[3][4]

In the HTML5 draft, there is no presentational element for strikethrough. However, there are two related semantic elements. Firstly, <s>, that is strikethrough in HTML 3 and 4, is redefined to mark text that is no longer correct, and secondly, <del> marks text that has been deleted, as it does in HTML 4.01.[5][6]

In cascading style sheets (CSS) strikethrough is controlled using the text-decoration property, and specified by the line-through value of that property. For example, <span style="text-decoration: line-through;">ABCD efghi</span> renders like this: ABCD efghi

In plain text scenarios where markup cannot be used, Unicode offers a number of combining characters that achieve similar effects.

The “combining long stroke overlay” (U+0336) results in an unbroken stroke across the text:

while the “combining short stroke overlay” (U+0335) results in individually struck out characters:

Similarly, the “combining short solidus overlay” (U+0337) results in diagonally struck out letters:

as does the “combining long solidus overlay” (U+0338), which produces longer diagonal strokes:

A number of characters that have the visual appearance of struck-through characters exist in Unicode, including ƀ, Đđ, Ǥǥ, Ħħ, Ɨɨ, Ɉɉ, Łł, Ɵɵ, Ŧ, ʉ, Ƶƶ, ƻ, ʡ, ʢ, Ғғ, Ҟҟ, Ұұ, Ҍҍ. These usually have specific functions (for example, in the Latin Extended-A character set) or representations and are not intended for general use. However, they are not precomposed characters and have neither canonical nor compatibility decompositions. This issue has created security considerations since "precomposed" characters like U+019F and sequences like U+004F U+0335 or U+004F U+0336 often cause visual confusion (compare Ɵ and O̵ and O̶). Unicode has acknowledged this issue and has proposed a standardized method for counteraction.[9][10]

Double strikethrough is an option in certain word processing applications such as Microsoft Word. There is no generally agreed meaning of double strikethrough, but it may be used as a second level of single strikethrough.

In Japan, double strikethrough is conventionally used (rather than single strikethrough) when striking out text. This is for added clarity, as in complex kanji a single strikethrough may be missed or confused with a stroke in the character.

Double, triple or multiple strikethrough may also (especially formerly) be used as a way of emphasising words.

Since at least 2014, researchers in the area of optical character recognition have attempted to solve the problem of recognizing struck-out text in handwritten documents.[11][12]