A Starfleet battle fleet of the Dominion War that was all but wiped out in the Tyra system in early 2374, with only fourteen of its one hundred and twelve ships returning.
The Seventh Fleet is one of the numbered fleets into which Starfleet organised its forces during the Dominion War. It is remembered for one of the worst defeats of the war's opening months.
In the Deep Space Nine episode A Time to Stand, set three months after the Dominion captured the station, the crew of the Defiant wait at Starbase 375 for word of the fleet, which had been sent to halt the enemy advance at the Tyra system. The news is grim: of one hundred and twelve ships, only fourteen have made it back.
The loss underlines how badly the war is going for the Federation and Klingon forces, and it is against this background that Admiral Ross sends Sisko behind the lines in a captured Jem'Hadar ship to destroy the Dominion's ketracel-white depot.