It's a corner of a room, as seen through a pentagonal hole. The pentagonal hole is the planar pentagon ABCFD. The corner of the room is at E, where 3 planes mee

It's a corner of a room, as seen through a pentagonal hole. The pentagonal hole is the planar pentagon ABCFD. The corner of the room is at E, where 3 planes meet. ED, EF and EB are the visible parts of the edges where two of the planes meet. The only constraint on the shape of the pentagonal hole is to be possible to be positioned such that, from the viewer point of view, the vertices B, F, D to be seen as if they are on the edges of the room corner.