A 'sum' is a sequence of terms joined by addition.

A 'product' is a sequence of terms joined by multiplication.

Is there a general term for terms joined by a general associative operation, that mathematicians would know? Is it 'sequence'?

In Haskell this would be implemented as a fold, but what do you call the thing it acts on? 'Iterable' and 'Enumerable' are too computer-sciencey.

It's possible this question has no good answer.