A unit cell is the smallest repeating unit in a crystal lattice that reflects the overall symmetry and structure of the entire crystal. It is defined by its dimensions and the angles between its edges, which can vary depending on the type of crystal system, such as cubic, tetragonal, or hexagonal. The unit cell contains the arrangement of atoms, ions, or molecules that make up the crystal. Unit cells can be categorized into two main types: primitive and non-primitive. A primitive unit cell contains only one lattice point, while a non-primitive unit cell contains more than one. Understanding unit cells is essential in fields like materials science and solid-state physics, as they help explain the properties of various materials.