Sybaron

Sybaron is a star system in the Alpha Quadrant. During the Dominion War, the system was held by the Dominion.

In 2374, the Starfleet 7th Fleet launched an offensive against the Dominion forces in the system, but were beaten back, having being unaware of the true scale of the enemy numbers.

Several days later, the Dominion launched a counter-offensive, inflicting more casualties on the Federation Alliance forces. The 7th Fleet held, although just barely. 

The 7th Fleet was at half-strength several weeks later due to the attack on Sybaron when they were sent to stop the Dominion at the Tibor Nebula.