How do you explain if something IS NOT a perfect square / square number?

A square number cannot be a perfect number. 0, 1, 5, 14, 30, 55, 91, 140, 204, 285, 385, 506, 650, 819, 1015, 1240, 1496, 1785, 2109, 2470, 2870, 3311, 3795, 4324, 4900, 5525, 6201 ... The sum of the first odd integers, beginning with one, is a perfect square: 1, 1 + 3, 1 + 3 + 5, 1 + 3 + 5 + 7, etc.

Answer: Suppose √64 = 8, Here 64 is the perfect square number. It gives 8 as the answer which is a natural number. So we call 64 as a perfect square number. Based on this I conclude the numbers which give decimal form an answer when they are under root those are considered to be not a perfect square number.