Perfect Square

A number made by squaring a whole number.

Here are the first few perfect squares:
0 (=0×0)
1 (=1×1)
4 (=2×2)
9 (=3×3)
16 (=4×4)
25 (=5×5)
36, 49, 64, 81, 100, 121, 144, ... and so on

Also known as "Square Number".