A quick run down:
If you're just fucking around, you have an open relationship. If you're fucking around with non-romantic friends, it's FWB--which is part of an open relationship. If you're engaged in building romantic relationships, it's poly.
Note: you can do all of those at the same time. You can also engage in an open relationship for some time while trying to find additional romantic partners, which is also poly.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.