A regular, periodic three-dimensional arrangement of atoms, ions or molecules indicating their positions in a crystalline solid.
There are 14 unique, repeating arrangements of lattices, known as Bravais lattices. All crystalline materials recognized today, not including quasicrystals, fit in one of these arrangements. These define the fundamental translational symmetry of all crystals, and together they form the seven crystal systems – Cubic, Tetragonal, Monoclinic, Orthorhombic, Triclinic, Hexagonal, Trigonal.