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.
Whether the interval used is open or closed, and at which ends, is at the discretion of the user of the term, who should make it clear which precise definition they are using.
However, the term unit interval is most usually used to refer to the closed interval [0,1], and Wikipedia follows this convention.
Squares within these windows represent the units in the network, but most windows will appear completely fl at first because the units begin at their resting activation, which is 0 for most units.
For layers of relation units, the square are arranged in groups of five, surrounded by a magenta border, each representing a single relation unit.
The brightness of the square depicts the magnitude of the activation: maximum brightness corresponds to the maximum activation of the unit, and fl corresponds to an activation of 0.