I announced it on my DevLog when I added it, but I'll mention it here as well: We now have tagging on the WarFoundry dev site.
Tags, as with their uses in other places, are basically a way of identifying common themes between things. The Trac tagging applies to tickets and wiki pages and is just a list of space separated words. The tags page then lets you pick a tag or search tags. The system is also set up to use two values from tickets as tags (the status and the component) so all tickets will be tagged in some way.
Tags can be added when creating tickets (available to anyone who is registered as "keywords"), when editing a ticket (available to developers: me, darpified and gregmita) or when editing a wiki page (available to developers and documenters: me, darpified, gregmita and snowblizz).