Antiprism

Like a prism it's two ends are identical polygons, but one polygon is rotated relative to the other before the two are connected by a band of alternating triangles.

Here is an octagonal antiprism: there are two identical parallel octagons, with a small rotation, then they are joined by triangles.

The rotation is usually 180°/(number of sides), so the octagonal antiprism has a twist of 180/8 = 22.5°.

Below is a square antiprism, with a 180°/4 = 45° twist.