Noun
Penrose triangle (plural Penrose triangles)
English Wikipedia has an article on:Penrose triangleWikipedia
An optical illusion depicting an impossible solid object made of three straight beams of square cross section which meet pairwise at right angles at the vertices of the triangle they form.
The term "Penrose triangle" can refer to the 2-dimensional depiction or the impossible object itself. Source: Internet
This was illustrated with the Penrose triangle and Penrose stairs. Source: Internet