examples of pleats
Pleats: creases in fabric giving volume to a curtain.
inverted pleat 
Pleat formed from two pleats that meet on the reverse of the fabric.
pinch pleat 
Pleat formed from three pleats stitched together at the bottom to keep them together.
box pleat 
Pleat formed by two folds that meet in front and touch on the outside of the fabric, thus forming a hollow in the fabric.