A quantity representing the power to which a fixed number (the base) must be raised to produce a given number.
A logarithm answers the question "How many of one number do we multiply to get another number?"
Example: How many 2s need to be multiplied to get 8?
Answer: 2 × 2 × 2 = 8, so we had to multiply 3 of the 2s to get 8. We say the logarithm of 8 with base 2 is 3.