any of 14 possible three-dimensional configurations of points used to describe the orderly arrangement of atoms in a crystal. Each point represents one or more atoms in the actual crystal, and if the points are connected by lines, a crystal lattice is formed; the lattice is divided into a number of identical blocks, or unit cells, characteristic of the Bravais lattices. The French scientist Auguste Bravais (Bravais, Auguste) demonstrated in 1850 that only these 14 types of unit cells are compatible with the orderly arrangements of atoms found in crystals.

The lattices listed by Bravais are divided into six or seven major crystal symmetry systems. All crystallographers recognize the isometric (isometric system), orthorhombic (orthorhombic system), monoclinic (monoclinic system), tetragonal (tetragonal system), triclinic (triclinic system), and hexagonal systems (qq.v.); some, however, define the hexagonal system so as to include the trigonal or rhombohedral system, which is considered a seventh system by others.