Common Logarithm (Base 10)

The common logarithm uses base $10$ and is written as $\log(x)$ or $\log_{10}(x)$. When you see $\log$ without a base in math textbooks, it usually means base $10$.

For example, $\log_{10}(100) = 2$ because $10^2 = 100$. And $\log_{10}(1000000) = 6$ because $10^6 = 1000000$. The answer tells you how many digits the number has (roughly).

You see this less often in CS, but it appears in scientific computing and data analysis when working with powers of $10$.