In a crystal, a cell C', which is obtained from a unit cell C by removing one or more translation vectors, is called a supercell of the cell C.
When dealing with large crystal systems, the unit cell is splitted into smaller subcells, and then the unit cell is filled by replicating the subcells.
For instance, the intense diffraction spots in the SAED pattern of La3Cu2VO9 taken along  zone axis in Figure 3561 were originated from the hexagonal subcell (a ≈ 4 Å, and c ≈ 11 Å).
Figure 3561.  SAED patterns of La3Cu2VO9. 
 Sylvie Malo, Douglas A. Vander Griend, Kenneth R. Poeppelmeier, Yanguo Wang, Vinayak P. Dravid, Crystal symmetry of La3Cu2VO9 and La4Cu3MoO12 derived from the YAlO3 hexagonal structure by transmission electron microscopy, Solid State Sciences 3 (2001) 17–23.