UPDATE: Now it should work in QCDE multiplayer servers. And not only for QCDE. Should work with other mods too. If you notice something wrong, tell me...
You can tag anything on ModDB on ModDB, and all tags can be voted up/down by the community depending on their relevance.
Official tags, as well as up-voted tags will appear higher in the list as they are deemed the most relevant.
If you discover a page that does not have any tags applied, why not help out the community by submitting tags, or posting a comment with #tags in it, which will be automatically linked.