A "typo" is a mistake made in typing, usually resulting from a slip of the fingers, confusion over similar-looking letters, or incorrect spelling. Typos often occur in written documents, text messages, and online posts, where the author may unintentionally type the wrong character or misspell a word.
The term "typo" is a short form of "typographical error," which originated from the practice of typesetting in printing. Its usage has evolved, but it still retains the essence of an error related to typing.