Example: In Battlefield:Modern Combat, one Achievement acquired by hitting 5 enemies and 0 friendlies in one mortar strike. This is doable but, during normal play, exceptionally hard. Boosting would be getting 5 people you know to join the other team and all stand in one place so you could drop a mortar strike and get the achievement.
Other boosters: Yeah, we're ready.
Me: *runs around killing all the noob boosters while they don't suspect it*
Booster: Hey stop, we're trying to do something!
Me: You guys are losers for boosting. Get a life and play the game the way it was meant to be played!
friend2: Easy! We can invite all of my friends to join a match. They can just sit there while u kill them over and over for easy kills!
friend1: So you mean boosting?
friend2: Yup my friends have all the achievements anyway!