A typo is a mistake in written or published writing. If you find a misspelled word or misplaced punctuation mark in this blurb, you've caught a typo.
Typo is short for typographical error, and you can also call it a misprint. Typos are errors made during the typing process that have been missed by editors and proofreaders. Originally, typos were mistakes made during typesetting, but today you can use the term for mistakes in any typewritten text, from instant messages to social media posts.