User blog comment:Holomanga/Introduction to Verfs/@comment-26335203-20170114134141/@comment-88.110.253.12-20180717190428

This is how wikipedia explains it;

Imagine a plane intersecting the cube and cuttuing off one of the vertices; what shape would you leave behind once the vertex has been cut off? For a cube it would be a triangle, for an octahedron, a square etc,

https://en.wikipedia.org/wiki/Vertex_figure