VIP
From Halopedia, the Halo wiki
VIP is a new gametype in Halo 3. Each team is assigned a "VIP" which they must protect while trying to kill the other team's VIP. Each team can only score by killing the opposing VIP. Whoever kills the VIP will become their team's VIP after their next respawn. This might also be what the "leader" is in the also new game type Escort.