On this feature request, I believe it would be useful to allow tag creators to add a brief description of what the tag entails. This is helpful for new team members or to remind people of what a tag means in the context of that board. (.i.e: Blocked)
When hovering the tag, a pop-up could be displayed showing that description (as it does when you roll over a user). This way, if a user doesn’t quite remember what Blocked’ really is, when hovering that tag, a description appears (‘tasks which are depended on other tasks for being completed’).
This was just a silly example, but I hope you can understand the main motivation for this feature.