As macmil says "AR" is usually a generic term for abrasion resistant plate and the "360" is the Brinell hardness.
In most cases these steels are not made to a "standard" but according to the specifications of the steel mill that produces it. "360" used to be a common figure, but in a lot of cases that has been replaced by "400", although 450, 500 even 600 are now available.
Typically the steels up to 500 are low carbon, low alloy steel (frequently Boron treated), produced as plate, quenched and tempered during the rolling process.
Search for the Swedish Steel "Hardox" web site for useful information.