A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor promoting corrosion of the cooling system, however some coolants can be quite toxic if inhaled.
When the Daedalus was affected by a Wraith computer virus, Dr. Lindstrom and Meredith Rodney McKay were both exposed to coolant by the entity as a means to distract them from discovering it. Dr Lindstrom got a bigger dose and vomited from exposure while McKay's exposure wasn't bad. (SGA: "The Intruder")
Adria once used her mental abilities to vent coolant on the Odyssey into a chamber that Dr. Daniel Jackson was trapped in, attempting to distract the rest of SG-1 from getting to her. (SG1: "Dominion")