"Heroic Missions: Heroic missions are more challenging than one player can handle alone. You will need to call in a friend or two to help. Some heroic missions will need a full group of four players in order to succeed.
Flashpoints: Flashpoints are action-packed, story-driven adventures that test a group of players to their limits, putting them up against difficult foes in volatile situations. Flashpoint missions take place in private story areas and most are balanced for a full group of four players."