Square or triangle elements are mostly used to generate a mesh for a simulation.
When two or more nodes of one element fall on the same coordinate the element is called a degenerated element.
This way a square can become a triangle, a line or even a point.
Depending on the used program the multiple nodes will be joined automatically to one node or need to cleaned up manually.
Degenerated elements exist in volume elements as well.
A hexahedron can degenerate to a prism or tetrahedron.
Degenerated elements lead to wrong results in the simulation or even block the start of an simulation.
This glossary of plastic industry is provided by PLEXPERT Canada Inc.