a space between the two front teeth on the upper row of teeth in a male or females mouth. having a gap is considered a sex symbol (like beauty marks) and attractive. Recently, having a gap has been associated with overly sexual people, so to hear a girl being called a slut because she has a gap is not uncommon. Gaps are cute on girls and modelesque on men. Most people with gaps are sexually attractive.
Lara Stone, Tyler Fuchs, Anna Paquin, Michael Strahan, Madonna, Georgia May Jagger. All have gap tooth mouths.