A PyMOL representation is merely a geometric derivative of some underlying data object or property (e.g. atoms, bonds, lattice, volumes). By adjusting various settings, it is possible to improve the quality of the rendition.
This links are not yet complete, so for the time being, please refer to the Representation Category on the PyMOL Community Wiki.
Atoms: dots | spheres | mesh | surface | nonbonded | nb_spheres | labels