Square numbers are numbers that have square roots that are whole numbers. In other words, when you take a whole number and multiply it by itself, you get a square number. For instance, if we take 5 and multiply it by itself, we get 25. 25 is an example of a square number.
A square root is the opposite. When you have a square number, you take the square root to find which number multiplied by itself gives you that number. That is it's square root. For instance, if we want the square root of 36, we look for a number that when multiplied by itself gives us 36. 6 would be the answer.