Def. 2. A face of a solid is a surface.
The first two definitions correspond to definitions I.Def.2 and I.Def.3 for a line and its ends, and definitions I.Def.5 and I.Def.6 for a surface and its edges.
Some examples of solids that appear in Books XI through XII are parallelepipedal solids (see proposition XI.24 and the following propositions), prisms (XI.Def.13 and proposition XI.39), pyramids (XI.Def.12, XII.3 and the following propositions), cones and cylinders (XI.Def.18 through XI.Def.24, XII.10 and the following propositions), spheres (XI.Def.14 through XI.Def.17, and propositions XII.17 and XII.18), octahedra (XI.Def.26, XIII.14), cubes (XI.Def.25, XIII.15), icosahedra (XI.Def.27, XIII.16), and dodecahedra (XI.Def.28, XIII.17).