Noun: A house party where in order to get in you have to either bring your own booze (BYOB) or pay the host to drink; usually done by trading off the rights to have a party at the host's house as long as he or she gets profit or free alcohol/substances in the process.
"Hey dude, you want to hit up this party tonight? It's better than just sitting around here."
"I don't know, is there going to be alcohol?"
"Yeah dude! Well, no... Only if you bring it yourself or you pay someone to drink theirs."
"So you're saying it's a freeload party..."
"Then no, those are fucking lame."