There are a total of six parameters that characterize a unit cell.

i. Dimensions of a unit cell (also called the edges): a, b and c.

ii. The angles between the edges: α, β and γ

The variation of these 6 parameters leads to different shapes and sizes of the unit cell, shown as below:

Where a, b and c are technically the vectors of the unit cell. The angle α is between edges b and c; the angle β is between the edges α and γ; γ is the angle between a and b.