An inverted pleat is a box pleat sewn in reverse and a box pleat is a combination of 2 knife pleats made back to back. So it is all in the family of pleats. To put it in simple words, inverse pleats are what you get on the back of a box pleat.
But the look of an inverted pleat is quite different from that of box pleats or any other pleats. For one, they are not in-your-face. An inverted pleat very unobtrusively contains the fullness and gives generous ease for comfort and decoration.
To make an inverted pleat, you will need three times the fabric that you normally need. ie if you want to sew a 2 inch wide inverted pleat you will need to take 6 inches fabric.
How to sew an Inverted pleat
Mark 5 lines equidistant from each other on your fabric.ie if you want a 2 inch inverted pleat, mark 5 lines 1 inch apart on 4 inches total area.
Now you will have to fold the fabric at lines 2 and 4 and bring this to meet at line 3; ie the folds of the pleats you make on either side is brought to meet at the center.
Fold the other side also to meet the 3rd line.
You can baste stitch your folds in place, before you sew the folds in place.
Sew across the folds as in the picture above, catching the pleat edges. When you reach the end of the stitching of one edge, you will have to pivot the fabric keeping the needle in the fabric and make 3 stitches across the fabric and then pivot again and stitch the next edge.