As far as I know they are used interchangeably and mean the same thing, at least as we are discussing. I'm sure I'll get a butt chewing from some electrician about it, but as long as you aren't mixing up serial / parallel I think we will be ok.
And don't use cereal instead, doesn't work, for a variety of reasons.
Maybe it comes from some of our computer days, serial ports, parallel ports.
The two words are used interchangeably. Although I often think of serial as a more sequential process as in using a battery set one at a time in a certain order as in having a serial number. And again in the context of batteries the two words have same meaning.
I think for clarity for circuit components (batteries, PV panels, etc) it is better to stick to using the term series, and to phrase sentence structure accordingly.