Think about objects in Object Mode as containers of stuff. So a cube is a cube in object mode, but as soon as you go into Edit mode, the cube is just vertices, edges and faces floating somewhere in 3D space. Then you tap out to Object Mode again and it becomes a cube again. So the vertices, edges and faces are being contained inside the cube, the cube is a container of vertices, edges and faces. You go in to the cube to mess round with its contents, and move stuff around. And it just so happens that the contents inside are arranged in a way that it has the shape of a cube and we call it a cube. But in reality what the cube really is is an arrangement of vertices, edges and faces in 3D space.
