A
typographical error (often shortened to
typo) is a mistake made in the
typing process (such as a spelling mistake) of printed material. Historically, this referred to mistakes in manual
type-setting (
typography). The term includes errors due to mechanical failure or slips of the hand or finger, but excludes errors of ignorance, such as
spelling errors. Before the arrival of printing, the "copyist's mistake" or "scribal error" was the equivalent for
manuscripts. Most typos involve simple duplication, omission, transposition, or substitution of a small number of characters.