Inseam is the measurement of the inner leg seam of a pair of jeans, running from the crotch down to the bottom of the hem. Together with the waist measurement, it forms the two numbers commonly used in jeans sizing, such as W32 L34, where the L figure is the inseam in inches.
Getting the inseam right affects how the hem sits relative to your shoes: too long and the fabric pools or drags on the ground, too short and the ankle shows more than intended. Since leg openings and rise both influence how much break or stack appears at the hem, the same inseam number can look different across cuts and styles.
Many retailers offer several inseam lengths for the same style and waist size, and hemming is always an option if nothing available is an exact match. See our jeans size guide and how to hem jeans guide for adjusting length after purchase.