A logarithm is the inverse operation of exponentiation. The logarithm of a number \(N\) to the base \(b\), written as \(\log_b N\), represents the exponent to which the base must be raised to produce the number \(N\). That is:
\[ \log_b N = x \quad \text{means} \quad b^x = N \]
This is valid for: \( N > 0, b > 0, b \neq 1 \)