Social dancing too. Most major cities have at least some scene for each of swing, salsa, ballroom, and tango. And typically you can actually hear people over the music, so it is actually possible to go and socialize, and it's perfectly acceptable to show up alone, without a big posse.

That said, if you do this, please do not be creepy— at least in the swing dance scenes I was involved in in (Toronto, Seattle, New York), the overwhelming majority of people were there to have fun dancing, not to hook up or be hit on.