1) Skirt insert 2) Triangular insert 
[sewing] A godet (eɪ or t) is an extra piece of fabric in the shape of a circular sector which is set into a garment, usually a dress or skirt. The addition of a godet causes the article of clothing in question to flare, thus adding width and volume. Adding a godet to a piece of clothing also gives the wearer a wider range of motion. ...
triangular piece of cloth inserted in a skirt
A godet is a triangular piece of material inserted into a garment, such as into a skirt to create a flare.
A triangular piece of fabric used as an insert in the seamline to provide freedom of movement or to enlarge a sleeve opening.
A triangular fabric piece placed into a hem to give fullness (e.g., the bottom of a skirt).
a triangular piece of fabric, often rounded at the top, inserted in a garment to give fullness. Cf. gore (def. 1),(def. 1). · a glass or plastic roller for guiding synthetic filaments into the centrifugal box.
A triangular piece of fabric inserted into a skirt to widen the bottom to add movement and fullness. Is also used in sleeves and bell-bottomed pants.