pleat vs crease

A pleat (left photo) involves the cloth folded back on itself, accordion style. It's one of the ways to make a garment wider or narrower in parts, rather than just being a cylinder. For example flaring a skirt, or bringing in the waist of pants.

A crease (right photo) is a line on fabric that might have been ironed in, or might just be a wrinkle from how it's been worn or stored.

There are also creases on your hands, around your eyes, and in other non-clothing items, so it might be used for metaphorical effect.

A pleat is always deliberate. A crease isn't necessarily so.