A crescent is a thin, curved shape that’s thicker in the middle and tapers to thin points at each end, like the little sliver of moon you might notice in the sky.
Crescent was first used to describe the shape of the waxing, or growing moon, and if you listen closely you can hear its similarity to increase. But a crescent can be any thin, curved shape. You might see a crescent of light hitting the pavement or a crescent of beach next to the ocean. Crescent can also act as an adjective describing something that has that shape, like a crescent moon or a crescent roll.