A social gathering of people, usually by invitation, but sometimes the host or hostess is nice and lets anyone come to the party. These are the best kind of parties.
A good party usually involves a fair amount of debauchery, sex, drug abuse, alcohol, and vomiting. Additionally, a good party sometimes won't end for several days, long after the host has passed out and/or returned to work. At a really good party, the original guests may be gone by the time the party is over.
Some other kinds of parties (the more boring kind), include political parties, travelling parties, and the other kinds that are covered in the other entries on this node.