A crystal-class system , or
Crystal systems in two and three dimensions
In the two-dimensional space there exist four crystal systems:
In the three-dimensional space there exist seven crystal systems:
Note that the adjective rhombohedral refers to a lattice system, not to a crystal system. Rhombohedral crystals belong to the trigonal crystal system, but trigonal crystals may belong to the rhombohedral or to the hexagonal lattice system.
Section 8.2.8 in of International Tables of Crystallography, Volume A