This dataset is described on its dumps download page
This dataset is a compressed format of the best pageview data that the Wikimedia Foundation had at any point in its historyː
- From 2007 to December 2015, it compressed the pagecounts-raw dataset, which is now deprecated
- From Dec 2015 to Present day, it compresses the pageviews dataset
More information about each of those datasets can be found on their pages.