El-Gatark was a location in the Alpha Quadrant. It was located near to the border between the United Federation of Planets and the Cardassian Union.
El-Gatark was the site of a battle between the USS Valiant and a Cardassian battle cruiser in the early days of the Dominion War. (DS9: "Valiant")
This location was only mentioned in dialogue.
This location's quadrant of origin is inferred based on the position of the Cardassian Union as seen in the star chart appearing in the Star Trek: Picard episode "Maps and Legends". The Star Trek Encyclopedia (4th ed., vol. 1, p. 230) placed El-Gatark in Federation territory. It might have been located in the Kepla sector, for the reason that acting captain Tim Watters never mentioned the Valiant leaving this sector just before the battle.
According to Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), El-Gatark was a star system. The system's primary was a M-class star.