A logarithm is a mathematical function that helps us understand how many times we need to multiply a certain number, called the base, to get another number. For example, in the expression log_b(a) = c, b is the base, a is the number we want to reach, and c tells us how many times we multiply b to get a. Logarithms are useful in various fields, including science and finance, because they can simplify complex calculations. They also help in solving exponential equations, where the unknown is an exponent. Common bases include 10 (common logarithm) and e (natural logarithm).