Quad
A four-vertex face, the modeler's preferred polygon.
A quad is a face with four vertices. Quads are the standard working polygon because they subdivide predictably, deform cleanly in animation, and form readable loops across a model. Good topology mostly means well-organized quads.
Related: Tri (Triangle) · N-gon · Edge Flow
These fundamentals are covered hands-on in Blender Geometry Essentials 01, free with a free account.