The correct answer to this open question is the following.
The term that defines the smallest piece of a crystal that shows the shape of that type of crystal is "unit cell."
In the atomic world, the smallest portion of a crystal lattice is a unite cell. A unit cell shows the 3D or three-dimensional pattern of the crystal. So this unite cell can repeat itself to form the crystal lattice. There are cubic cells, monoclinic cells, tetragonal cells, orthorhombic, cells, and rhombohedral cells.
