To begin determining the Mean Squared Logarithmic Error (MSLE), we take the natural logarithm of each predicted value. Use the values to determine the mean squared error, also known as the Mean Squared Logarithmic Error. Another way to look at it is as a comparison of the observed data to the expected outcomes.
Source: https://insideaiml.com/blog/MeanSquared-Logarithmic-Error-Loss-1035