Logarithm
The exponent to which a base must be raised to produce a given number.
A logarithm answers the question “to what power must the base be raised to get this number?” So log_b(x) = y means b^y = x. Common bases are 10 (log), e (natural log, ln), and 2. Logarithms turn multiplication into addition and compress huge ranges, which is why they appear in pH, decibels, the Richter scale, and algorithmic complexity.
Example: log₁₀(1000) = 3, because 10³ = 1000.