Classic Rush; AKA Crush - Classic rush is when you make the character you want rushed in non-expansion. ( Cant be Druid or Assassin ) and rush him to act 4 hell, then convert to expansion and you will be in act 5 hell in expansion.
Benefits of Crushing over Grushing - You can still be a bumper for Norm and NM.
Glitch Rush; AKA Grush - Glitch rush is when you get someone who hasn't done theyre baal quest, and you stay in town while they do baal. It glitches your quest, and you can go to the next difficulty.