Vertex

A vertex is a corner where sides or edges meet. Its plural is vertices, not “vertexes”. A square has four vertices.

A vertex is a corner; the plural is vertices. In a flat polygon, straight sides meet at vertices. In a solid, an edge is where two faces meet, and a face is a flat surface.

On a cube, an edge is the segment where two faces meet, and a vertex is a corner where edges meet. The cube has 12 edges and 8 vertices; the flat face you can see is only a bounded part of a plane.