UPDATE: Thank you to commenter Victoria of Love Fashion Love Vintage. These are called organ pleats because of the way they resemble the pipes on an organ. While I agree that this fabric has body, I don't think it is a heavy velvet or corduroy. And while there is likely some type of inner stiffening, the shape of the pleats cannot come from that alone, else the skirt would just flare out and not fall into those rounded shapes. You can see in the second photo that each pleat is a separate gore. And if you could see the inner construction of the skirt, you would likely find some type of tape sewn from gore seam to gore seam at the upper third of the skirt. The tape would be smaller in circumference than the skirt itself and would hold the lovely rounded shapes up and away from it. Does that make sense?
