What does it mean to say that a number is a perfect square

Answer 1

It has to be the result of some number multiplied by itself
e.g. 6*6 = 36, so 36 is a perfect square
The square root of a perfect square will be a rational number.
A perfect square could be a whole number, a decimal number or a fraction

e.g. 1.44 is a perfect square, since √1.44 = 1.2 exactly
81/169 is a perfect square since √(81/169) = 9/13 exactly

A perfect square cannot be negative.