An operating table was a flat surface on which surgical procedures were performed.
Awaiting surgery on his brain, a time traveling Pavel Chekov lay on an operating table at Mercy Hospital just prior to being rescued by James T. Kirk, Leonard McCoy, and Gillian Taylor. (Star Trek IV: The Voyage Home)
In 2375, Ezri Dax described her transformation after becoming joined with the Dax symbiont as laying down on the operating table one person and waking up a completely different person. (DS9: "Shadows and Symbols")