In mathematics, the logarithm is the inverse of the exponential function. It is a way of expressing a number as an exponent of another number. The logarithm of a number x to base b is denoted as logbx and is defined as the exponent to which b must be raised to obtain x. For example, the logarithm of 1000 to base 10 (written as log101000) is 3, because 1000 = 103.