Tags are titles which are granted by Mur or the Council for extraordinary effort in a special field. Additionally, the kings and queens can grant them on land related matters, Chewett for forum related matters, and Zleiphneir in all matters that concern Bob the Tree (see Defenders of Bob). Those tags are visible as orange text on the mini-profile in game, and get added to the headline of you profile.
Most tags come together with a description of the role, but those are only visible by players of the same Mindpower due to technical matters and on the profile.