I am not sure if the mathematical physics tag would be appropriate for this post:
I) Yes, it seems the mathematical-physics tag applies to fractional derivatives, in particular since fractional calculus is a relatively advanced mathematical discipline, which is rarely covered in a standard university curriculum.
II) More generally, for the most common tags insert-tagname-here, there is:
a short pop-up wiki tag excerpt available by hovering the mouse over the tag in the main Phys.SE site, or
a longer wiki tag description at https://physics.stackexchange.com/tags/insert-tagname-here/info,
where one can learn more about the insert-tagname-here tag. If not, then users are encouraged to create a wiki tag description (or improve an existing wiki tag description).