Briefs are a type of short, tight underwear and swimwear, as opposed to styles where the material extends down the legs.
A main difference between male briefs and female briefs is that male briefs are often designed with a seam or much larger pouch in the crotch area to accommodate a bulge. This is because men and boys have larger external genitals in comparison to women or girls, thus requiring more fabric in the crotch area.
See swim briefs for the case of briefs as swimwear.
Underpants are a man's undergarment covering the body from the waist or hips to the top of the thighs or knees.