It’s easy to define Flat Front pants as pants without pleats. But what are pleats anyway? A pleat is a fold created in fabric by doubling it up on itself and then holding it in place. You’ll see pleats in your pants mainly to facilitate the creasing process (see the image below):

You’ll generally find that American Suits will come with pleated pants and European Suits will come with Flat Front pants. If you’re wearing pleated pants, then you must also have a nicely planted crease. If you’re wearing flat front pants, the crease is optional. While it is true that 9 out of 10 times, you’ll see creases with suit pants (regardless of whether they are pleated or not), this does not have to be the case. Creases are synonymous with tradition while the absence of creases usually indicates a modern look. Not everyone can wear flat front pants well (i.e. you’ll need a slimmer figure to wear them well). If you’re wearing khakis or jeans, though, skip the crease.