"When people talk about swinging, do they generally mean:
- having sex as a foursome,
- having sex individually with other people, but in the same room,
- having sex individually with other people, but maybe in different rooms in the same house?"
From what I've heard, it's any or all of the above. The main thing about swing being the sharing of sex (as a single or with persons outside the couple) without the danger of falling in love (with said persons). There are also swing clubs but I hesitate to describe them in detail as I've no experience there.
Sounds like the thing to do for now is to cool it on poly until February or so. Of course you can still learn more about poly (and swing) in the meantime.