1. When the highschool alumni come to see a home football game. The week leading up to the Homecoming game can involve class spirit competitions and other such things.
2. Referring to the Homecoming football game.
3. Referring to the dance typically the night after the football game.

In high school: A meaningless football game, followed by a clothed orgy containing mostly lowerclassman.

The first dance (semiformal) held at the beginning of every year. Is for every grade, not just underclassmen. Is also a dance for the previous graduating class to come back and dance again, hence the name "home coming", like "coming home".

A dance at the beginning of the year that a lot of the school population uses as an excuse to drink a lot of alcohol ... a good time to make new friends, and do things you had always wanted to but never got the chance.
May have consequences.

A huge orgy involving multiple parties, grinding, and tons of drunk/horny teenagers that usually follows a football game.

a time for high school students to come together and rock the gym, grind on strangers, and dress up with friends

1. A pathetic excuse that freshmen and sophomores use to try to substitute Prom. Has a much lower rate of ending with poontang than Prom.