Definition
The vanguard of an activity.
How People Actually Use It
The act of walking into a fast-food establishment with a large group of 12 or so people and ordering a meal. After meal is prepared line up in a parallel line with the counter to distribute food. After distribution the leader of said group shouts "FIRE" at which the group throws the food back at the cashier, cooks, etc. Then upon completion of the act the group leaves the establishment.
"Leader: 12 Big Macs please. Cashier: Of course that will be insert amount here. (after receiving food) Leader: Would you mind if we form a line to better organize, a firing line if you will? Cashier: Not at all. Leader: Okay, so everyone's meals are correct? Group: Yeah. Leader: Right then, FIRE!"
Source: Urban Dictionary