A common logarithm is a logarithm with a base of 10. It is often written as log(x) or log₁₀(x), where x is the number for which you want to find the logarithm. The common logarithm answers the question: "To what power must 10 be raised to obtain x?" For example, log(100) equals 2 because 10² = 100. Common logarithms are widely used in various fields, including science, engineering, and finance, due to their simplicity and ease of calculation. They are particularly useful for solving exponential equations and for working with large numbers, as they can simplify multiplication and division into addition and subtraction through the properties of logarithms.