A pylon is a fixture on the aircraft, on which weapons or tanks are installed.
They contain explosive release units, which when activated, ensure positive separation of the stores attached to them from the aircraft.
Unless it is a Jaguar, then they removed the cartridges out of the pylons carrying the Jamming pod and Phimats as it was getting to expensive and producing a shortage with every man and his dog banging them off at the slightest wiff of a problem, thats if memory serves me correctly.