What is the meaning of Logarithm?

For a number $x$ , the exponent by which a given base number must be raised in order to obtain the power $x$ . Written $\log _{b}x$ . For example, $\log _{10}1000=3$ because $10^{3}=1000$ and $\log _{2}16=4$ because $2^{4}=16$ .