I studied algebra and group theory at the university about 20 years ago. Lately I've been reading the occasional maths book/article and they mention things like $\rm{SO}(n)$ and $\rm{SU}(2)$ as classes of groups.
I can see each of these are different categories of groups and remember studying these individually, however it seems these categories mean more now and are a part of some larger theory.
If this is the case, if someone could point me towards a reference / book (kindle would be good) it would be appreciated.
tia