What does boosted mean?

MMR Boosting (Match Making Rating, also known as LoL Boost is an act where a player (The Booster) logs into another player's account (The Boostee) to play a ranked game. While it is generally accepted that the intent of this is to improve the Boostee's MMR, any ranked game played by someone that is not the original creator of the account may be considered Boosting and as a result may be eligible for punishment.

Boosted means someone helped you get a higher rank. Like if a Diamond player says ''shit man im boosted!'' means he made a mistake and is making a joke about him playing bad.

On LoL it is a term used to describe a player who purchased assistance from a higher elo player to gain ranks in ranked play. Someone actually just boost for free for fun on their smurf accounts.

A player who "plays with a friend" until he reaches platinum, when he was originally in silver, is someone who is considered boosted. He goes on to play in plat elo, but isn't skilled enough to face those players, typically causing his team to lose.