is a special type of motor oil specially designed to lubricate car transmission systems. A higher viscosity then engine oil, transmission oils ensures healthy performance and ongoing protection for the gears and transmission system. It's not uncommon these days for some automatic systems to use pressurised hydraulic oil instead.
Whilst most modern transmission systems won't expect transmission oil replacement for 100,000 miles it's always worth keeping an eye on level and keeping it topped up. Take a quick look on line for a great choice of transmission oils for any car at Eurocarparts.com. Show Less