These are not to be confused with the tags that are displayed on the drawer area at the bottom of the right results pane of the Analyze panel, which display rule categories and applicable standards. Tag settings on the Rules panel instead refer to the bottom, left sidebar section of the Rules panel that allows you to select or deselect options to enable both best practice and/or experimental rules in the analysis engine. When selected, these run in addition to those that are a part of the active ruleset standard (and any custom rules, if present). Both experimental and best practice rules are subject to change, and the total number of each that is available are also subject to change with each new release of the axe-core ruleset.
Refer to the follow two subtopics for detailed information about each: