I've found the infinite-product tag but no infinite-sum tag.
Should infinite-sum be added as a synonym of sequences and series?
One thing I do not like about this possibility is that this name could also refer also to sums over arbitrary infinite set (not necessarily countable).
On the other hand, we do not have many question about this type of sum. (And to be honest, I am not sure what are "correct" tags for such questions.)