For questions about the favorite question feature or the favorite tags feature.

Favorite questions are marked by clicking the star below the question's score. It is searchable by using the infavorites:<user> query (where <user> could be mine to search your personal set of favorites). Favorite questions of any user are displayed in their profile in the favorites tab.

Favorite tags can be set in the prefs tab of your user page. Again, you can use intags:mine to restrict a search to your favorite tags. This feature was later renamed to tag watching or watched tags.

For more details see:

history | excerpt history