Hydraulic fluid referred to the liquids used by hydraulic machinery. In 2373, Alexander Rozhenko flooded an entire deck of the IKS Rotarran with superheated hydraulic fluid when he accidentally activated the hydro-static system pumps while the check valves were open. It took Alexander three days to clean up the mess, though he claimed it still smelled like burnt dog hair after he was done. (DS9: "You Are Cordially Invited")