Regularly spaced array of points that represents the structure of a crystal. Crystals are composed of groups of atoms repeated at regular interval in three dimensions with the same orientation. The smallest division of the lattice which can still be used to represent the entire structure is called the Smallest repeating unit of a crystalline solid that can be used to describe the entire structure. Unit cells are like templates which can be copied to produce an entire crystal.. Each such group of atoms is replaced by a representative point; the collection of points so formed is the space lattice or lattice of the crystal.
Some or all content above used with permission from J. H. Wittke.