Descriptions are very important because a title alone can be ambiguous and by itself may even have more than meaning (many words do).
I'm really not following your logic here, @Bryan. A definition is the perfect way to clarify the meaning of niche. What else is there?
A community may certainly develop around a niche, in that it has its own unique set of followers, but the niche itself is just a subject. That is the distinction. And the content posted to that niche is the important part. The niche itself also does not have a personality. It is simply intended to be a unique subject.