Crystal :

noun (from the Greek "krustallos", meaning ice) - A microscopic or macroscopic solid form of a mineral, bounded by faces, edges, and vertices, or by irregular borders.
A crystal develops through the ordered repetition in space of the smallest unit formed by the grouping of atoms in the mineral: the unit cell. (adapted from Foucault & Raoult, 2010, and Michel, 2016).

By studying the geometry defined by the repetition of unit cells in three-dimensional space, scientists have identified seven lattice systems (also known as the seven crystal systems in French literature).
These lattice systems are classified based on three axes that define the geometry of the polyhedron and the angles between those axes.