The square root of 125 is approximately 11.18. The decimals of the exact answer go on infinitely because the square root of 125 is an irrational number.
The square root of a number X is the number that, when multiplied by itself, gives X as the product. X is called the square of this number. The cube root of X is the number that produces X when it is multiplied by its square.
While the square root of 125 is irrational, the cube root of 125 is the rational number 5. Five times 5 is 25, and 25 multiplied by 5 is 125.