An inseam is the seam on the inside of the leg of the pants. The taller you are, the longer your inseam is going to be. Inseams usually come in even sizes, such as 28, 30, 32, 34 and 36.
The inseam measures the length of the leg on a pair of pants (or shorts or capris). It is measured from the joining seam at the crotch to the bottom of the hem.