Terminology:
Edge: a line segment between faces.
Face: any of the flat surfaces of an object.
Vertex: the corner of an object
Side: In a 2 dimensional shape, one of the line segments, or edges, in a 3 dimensional shapes, one of the faces
Symmetrical: A shape is symmetrical when it can be folded so that one part matches the other part exactly. The fold line is the line of symmetry.
Look at the pictures below for further explanation.
