The opposite of topless. Used for images where a character is not wearing lower-body clothing (ie pants, skirts, etc), but is still wearing some form of upper-body clothing. In the case of a one-piece swimsuit (and similar outfits) it is when the clothing does not cover the crotch.

A image can be tagged bottomless if the character in them is wearing panties or a swimsuit underneath their clothing. An image maybe in addition be tagged with nopan along with bottomless.

A image should not be tagged bottomless if the character is naked.

(Copied from Danbooru.)