'Snaggletooth' is an informal term for a single tooth that is noticeably out of alignment with the other teeth. This is usually due to what is technically known as a rotated tooth, usually in association with some type of crowding or malocclusion. This rotation around the tooth's long axis may be referred to as torsiversion or torsoclusion (the terms are synonyms). A snaggletooth may also be the result of an overgrown tooth, AKA macrodontia.
The term snaggletooth comes from the original meaning of the word 'snag', first recorded in 1577, when it was used as a noun. It originally referred to the stump of a tree or a branch, but was quickly generalized to mean any sharp or jagged projection. By 1585 the term 'snaggle-tooth' had entered the English language.
These days it is used infrequently, and when used it is often to refer to the cartoon character Snagglepuss rather than to dental disarray. When used to comment on the aesthetics of dentition, it generally refers to any tooth that pushes the lip out far enough for enamel to see the light of day, although teeth whose protrusion is only apparent during a smile may also be disparaged thusly.