Like in Profiles, it should be possible to add tags to a community. Why:
Value and relation of community to certain topic(s) is strengthened > how to find the most related community for topic XYZ when there are 50.000 communities?
crowd intelligence is used to allow multiple terms describing the same topic(s) that the community deals with > increases the chance to find the community
The amount of identical tags added should be reflected in search and tag cloud. Thus, tag population becomes a main criteria for showing the most relevant communities.
Community Managers (Owners) should of course be able to remove the tags added by others.