A party held during seasonal times, like Christmas, that involves heavy drinking, sex, and of course it's not a party unless there are drugs. Usuallly held be teenagers who know nothing but how to get completely shit faced.
You know you've been to a Jingle Jam, no example is needed, but then again you probably don't remember it, so here it goes.. It's that magical party held once a year by your tweaker friend as a way to get all those hot chicks to his house so he can legally mouth rape them with mistletoe. Remember, he told everyone to bring there own weed cuz he got tired of having to split it with everyone, but still ended up using most of everyon else's weed. Later on he ended up having a three-way with your sister and your girlfriend. Good times.. Good times...