A "Social" isn't really a "party". I guess they're similar, but a "social" is bigger. Typically, for a "social", they sell ticket for $5 or $10 to everybody they can. A lot of people buy them without intending to go, just to help support them. They have "social food" (usually sandwich meat, bread, pickles, cheese cubes, and little desserts) which is typically donated. They have a Silent Auction, where people buy tickets and put them in for each prize, then the prizes are drawn for. The prizes are also typically donated. Other than that, there's usually music, and dancing, and other boring stuff.
The whole "Social" is designed as a fund raiser. Usually, they are for people who are planning on getting married, to help pay for the wedding. They're a great idea, but for some reason, only people in Winnipeg do them.