Apart from the source (the content itself) the data about a current or old version of a page are as follows.
The edit metadata, the metadata of the edit that resulted in the particular version, are:
- If the edit was marked as a 'minor' revision by the editor
- Date and time the edit was made
- Page title
- Page namespace
- Username and user id, or IP address of the editor
- Comment left by the editor when the edit was saved
- Length in bytes of the revision content
- Sha1 sum of the revision content
- Revision id of the previous (parent) revision
- Content model of the revision (is it wikitext? json?)
- Content format of the revision
Other data about a page are:
- If the page is protected
- Page id (for old versions these are shown in the URLs of page history links)
- If the page is a redirect
- Whether the page is newly created or has more than one revision
- Id of the most recent revision of the page
- Length in bytes of the content
- Content model of the page
- Content language of the page
See en:Wikipedia:Edit summary#Places where the edit summary appears for lists of edit metadata.
For details see the documentation of the MediaWiki database.