Maybe some short explaination of it, or the way use the tag correctly.
Like example:

Iyashikei
Description
A healing series

^^ well mine is sucks, don't use mine
So while searching for series I understand what it means

Also, I have favorite categories, but I need to re-search on categories section all the time, is there a way to list my fav categories somewhere?

I was considering a hover option, where you give your mouse over a category and it shows the definition/meaning as a little pop-up box. It wouldn't be doable on mobile, though, unfortunately.

Perhaps a little question mark after the category name while on the category list page? It could open a tab or something? =/

I would just hope that any new feature is mobile-friendly, since people have largely shifted to using their phones for manga consumption and likewise are using MU on their phones.