A make-out party is a party where a people invite a mix of people their gender and the opposite. Often times, people at these types of parties might make out (kiss) with somebody other than their boyfriend/girlfriend. People who do that do it so rarely, that people stereotypically think that people only make out with their lover (or might kiss the lips). The only common exception to that is a romantic scene in a Hollywood movie.

Make-out parties can range from a massload of themes/circumstances for the party (e.g. 16th Birthday, Bachelor(ette), Dance, etc.) These kind of parties can trigger horniness. People who have a high-level of shyness (higher than average for their gender and age combined) may hesitate to make out but might dance with somebody that is the opposite gender.

People there might cook ordervs and some party toast. Some people who reach a certain level of horniness might persuade an opposite gender person to have sex (unless they are too shy). Other things that might happen at make-out parties would be people dancing with somebody in a sophisticated way (so sophisticated that it gets somebody to like somebody unless their high-level shyness acts as a blockade for that effect).