A typographical error (often shortened to typo), also called a misprint, is a mistake (such as a spelling mistake) made in the typing of printed (or electronic) material. Historically, this referred to mistakes in manual type-setting. Technically, the term includes errors due to mechanical failure or slips of the hand or finger, but excludes errors of ignorance, such as spelling errors, or changing and misuse of words such as "than" and "then". 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.

Fat finger or fat-finger syndrome (especially in the financial sector) is a slang term referring to an unwanted secondary action when typing. When a finger is bigger than the touch zone, with touchscreens or keyboards, there can be inaccuracy and one may hit two keys in a single keystroke. An example is buckled instead of bucked, due to the "L" key being next to the "K" key on the QWERTY keyboard, the most common keyboard for Latin-script alphabets.