For questions involving the "Ignored Tags" specified in a user's Preferences. Questions with these tags are dimmed or removed entirely from question lists.

For each Stack Exchange site, logged in users can specify "Ignored Tags" in their Preferences and directly from the Question list pages.

Questions with these tags are then dimmed or removed entirely (depending upon another preference shown on users/preferences/<user id>) from question lists.

See also: What do “favorite tags” and “ignored tags” do?