This window is the third part of a nice trio: search results, tags narrow down and selected tags. This window let's you see what tags were "narrowed down" and disable them one by one.
Remember that Calendar module records are very short. If you want a longer version of an event description you can always attach an article to a specific event. It can be a news article from your news feed or just a special article you wrote to make a story about what is gonna happen.