How can i pass edge nuity at this rate

What is the name used to describe a graph where for some value of x, there exists 2 or more different values of y?

The parabola opens: y=√x-4 (principal square root) up down right left

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.