Logarithm

the power or exponent to which a base must be raised in order to produce a desired number

Description
If a number, x, is expressed as a power of another number, y, i.e., if x = yn, then n is said to be the logarithm of x to base y. Common logarithms are to the base 10 or to base 2; natural or Napierian logarithms are to the base e, a mathematical constant.