sqrt(a) returns the square root of a. This means it returns that number which equals a, when multiplied with itself.

For example:

sqrt(4) = 2, because 2*2 = 4

sqrt(25) = 5, because 5*5 = 25

sqrt(100) = 10, because 10*10 = 100

Tip: If you need the cubic root or another n-th root, you'll find an explanation in the power section. There is also a code example.