A speech error, commonly referred to as a slip of the tongue (Latin: lapsus linguae, or occasionally self-demonstratingly, lipsus languae) or misspeaking, is a deviation (conscious or unconscious) from the apparently intended form of an utterance. They can be subdivided into spontaneously and inadvertently produced speech errors and intentionally produced word-plays or puns. Another distinction can be drawn between production and comprehension errors. Errors in speech production and perception are also called performance errors. Some examples of speech error include sound exchange or sound anticipation errors. In sound exchange errors the order of two individual morphemes is reversed, while in sound anticipation errors a sound from a later syllable replaces one from an earlier syllable. Slips of the tongue are a normal and common occurrence. One study shows that most people can make up to as much as 22 slips of the tongue per day.

Speech errors are common among children, who have yet to refine their speech, and can frequently continue into adulthood. When errors continue past the age of 9 they are referred to as "residual speech errors" or RSEs. They sometimes lead to embarrassment and betrayal of the speaker's regional or ethnic origins. However, it is also common for them to enter the popular culture as a kind of linguistic "flavoring". Speech errors may be used intentionally for humorous effect, as with spoonerisms.

Within the field of psycholinguistics, speech errors fall under the category of language production. Types of speech errors include: exchange errors, perseveration, anticipation, shift, substitution, blends, additions, and deletions. The study of speech errors has contributed to the establishment/refinement of models of speech production since Victoria Fromkin's pioneering work on this topic.