In b y = x, Then base b logarithm of a number X is given by logbX. Value of base can vary, we have three common versions log base 2, log base e, log base 10.
Log of X to the base b is how many times base should be multiplied by itself to achieve X.
Let's see this with an example if b = 5 and X = 25 the log525 = 2. that is we need to multiply 5 two times to get 25, and this is our log value.