Fleet- Any group of ships containing four or more capital ships assembled to fight an enemy. Typically in large fleet battles or to take/defend a planet or some other major goal.

Task Force- Any group of ships containing three or fewer capital ships assembled to fight an enemy. Generally in a raid or some other specific task.

Combat Group- A large group of non-capital ships assembled to fight an enemy. Usually designated as a system picket or a small raiding force, occasionally used to secure and deny shipping/supply routs to an enemy.

Wolf Pack- Five to six cruisers or battle cruisers that seek out targets of opportunity and engage them. Usually tasked with harassment of supply lines or small forces such as system pickets. Using hit-and-run and other tactics a pack can engage and take down ships several sizes larger than their weight class.

Flight- A very large group of fighters. Usually launched from a mothership or orbital hangers for planetary defense.

Wing- (1st deff) A large group of ships in a fleet containing its own command chain under the fleet commander's. A fleet can be divided into several wings each with its own goal and providing support for other wings.
(2nd deff) The second division in a large group of fighters.

Squadron- Third division of fighters, contains a few individual fighters.