Typo is a contraction of typographical error - or, in everyday English, a typing mistake. Every writer in English who uses a keyboard makes them. Professional printers sometimes call them literals - precisely, 'a misprinting of a letter' (as opposed to other forms of misprinting).
Some typos are fairly common. Some can be hard to see when you proof-read your own writing. So some of these are listed in AWE: see the category:typos