A number of content management systems allow for data to be classified using taxonomy (sometimes called categories or tags in a CMS). Most of us that use CMS and taxonomy aren't experts in how best to structure our vocabulary and usually end up with a mess of terms. In the end, we have a mess on our hand and wonder how best we should approach cleaning up the terms we're using.
A blog post by Lars Trieloff, The Art of Mining a Folksonomy, gives some great suggestions for cleaning up your taxonomy. The post was written for the Day's CQ5 CMS, but should be of use to almost any CMS user with taxonomy.