Upasampadā (Pali) literally denotes "approaching or nearing the ascetic tradition." In more common parlance it specifically refers to the rite and ritual of ascetic vetting (ordination) by which a candidate, if deemed acceptable, enters the community as upasampadān (ordained) and authorised to undertake ascetic life.
According to Buddhist monastic codes (Vinaya), a person must be 20 years old in order to become a monk or nun. A person under the age of 20 years cannot undertake upasampada (i.e., become a monk (bhikkhu) or nun (bhikkhuni)), but can become a novice (m. samanera, f. samaneri). After a year or at the age of 20, a novice will be considered for upasampada.
Traditionally, the upasampada ritual is performed within a well-demarcated and consecrated area called sima (sima malaka) and needs to be attended by a specified number of monks: "ten or even five in a remoter area".