It's simply a gathering of men and women to have a few drinks, maybe some hors deouvres, and some conversation.

Swim

Usually it refers to a party of hobbyists and providers as swim mentioned. There is a Meet and Greet board here on TER that discusses those.

However I wanted to mention that some folks use that same term to describe a meeting with a provider in a public location (such as a coffee shop) prior to heading behind closed doors. Some use that as a form of screening.