a square used as a standard for measurement of other objects. The dimensions of the square are of smallest base measurement of (cm, in., etc...)
A unit square is a square of side length 1.
a square that is one unit long by one unit wide
a square where each side has a length of one unit
The unit square in a Cartesian coordinate system with coordinates (x,y) is defined as the square consisting of the points where both x and y lie in the unit interval from 0 to 1.