Are there definitions or explanations for the categories? If I see a category which I'm not sure what it means I'd like to look after the meaning of it.
The genres have it so I thought the categories should have something similiar too but I didn't find anything.
Can someone help me?

Not really... They are supposed to be unspecific and broad. I doubt you are asking what vampire means but could you give some examples? They tend to be very descriptive like "friends become enemies". And if unsure what a certain word means, Google or a dictionary would help.

But yeah it wouldn't make much sense... Why explain to people what illness or childhood friend means?

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in need of romance?
uncommon, sad, sweet

vndb requires tag descriptions and they definitely have quite a few (mostly technical) that really need a description. Idk if the same can be said of MU tags though.

looking at that site... Yeah I guess you could create another section that explains these things. But then you should ask yourself if it's really worth to create descriptions when it would be along the lines of "AI Protagonist - One of the protagonists is an artificial intelligence." for like 95% of the categories...

That seems like so not worth it, it's hard to describe how much of a waste of resources that would be - and that's considering we have a review section that nobody uses and almost nobody even notices exists on the individual manga pages ?

________________
in need of romance?
uncommon, sad, sweet