These are 3rd party metrics provided by companies like Moz and Majestic that are generally based on the content on your site and the pages linking to your site.
For specifics on how the metrics are calculated, you can Google the metrics as there is plenty of literature on it.
There are a couple of important things to keep in mind:
- The metric is not what you should be optimizing for since the goal is to get rankings and traffic. The metric is a 3rd party's approximation of the value of a page.
- The metrics could have short term fluctuations for any number of reasons, including adjustments to the 3rd party's own algorithms. So I wouldn't worry about it too much.