A ward was a section of a hospital or other medical facility where patients were kept. Wards could be devoted to the care of either specific medical conditions or species.
While searching for Devidians in 1893 San Francisco at Sisters of Hope Infirmary, Jean-Luc Picard pretended to be replacing the burners on a gas lamp, as per city ordinances, so it would be safer in the event of an earthquake. When a doctor protested that there hadn't been an earthquake there in thirty years, Picard left the room, saying, "Well, that takes care of this ward." (TNG: "Time's Arrow, Part II")
In 2373, a Bolian orderly feared that half of a medical facility ward would be lost after Klingons took out the reactor during the Battle of Ajilon Prime. (DS9: "Nor the Battle to the Strong")
The wards on Hospital Ship 4-2 were known as levels. Patients were categorized by the Allocator using the treatment coefficient. (VOY: "Critical Care")