What exactly is the difference between these two tags? We aren't exactly going to deal with books that aren't novels here. Is there any difference? Should they be merged?
Obviously there's a difference: every novel is a book, but not every book is a novel. The question is, do we need both the more general tag and the more specific one?
We've actually been over this before. I was about to close this question as a duplicate of the 7-year-old one, but maybe it's worth having this discussion again: things have changed in the last 7 years, and indeed there are a couple of newer answers to the old question which have hardly had any attention.
This is what I said in my answer over there:
Split books into novel and short-stories.
Whether or not it makes sense to have media tags at all (a discussion that seems to be still ongoing), it's undeniable that books is a broader tag than the others. We don't have a screen tag to cover both films and TV, so why should we have a books tag to cover both novels and short stories?
If we get rid of books, then our media tags become less confusing and have no overlap:
But looking at this again now, I'd add that this would involve so much retagging that it's probably not worth doing. The books tag may be mostly redundant when we have both novel and short-stories (although it could still be useful for e.g. ID questions where the OP doesn't remember how long the story is), but it's not doing any harm. And it's certainly OK to have subtags and supertags, as for example we have tags for both star-trek and star-trek-tng, star-trek-tos, etc.
As was pointed out in comments, though (and also in CreationEdge's answer on the old thread), it may be that books is being used mostly for questions about novels. In this case, the issue would be relatively easy to solve, by merging books into novel and manually retagging those few questions which are currently tagged books but aren't about novels.