In the USA, it’s the Federal Aviation Regulation FAR 103 which defines the ultralight glider:
PART 103—ULTRALIGHT VEHICLES
§ 103.1 Applicability.
This part prescribes rules governing the operation of ultralight vehicles in the United States.
For the purposes of this part, an ultralight vehicle is a vehicle that:
(a) Is used or intended to be used for manned operation in the air by a single occupant;
(b) Is used or intended to be used for recreation or sport purposes only
(c) Does not have any U.S. or foreign airworthiness certificate; and
(d) If unpowered, weighs less than 155 pounds;
The american ultralight glider can only be a single seater, there are no airworthiness regulations, not any pilot license required, nor registration.
It has been admitted that the weight of a total recovery parachute system is excluded of the 155 pounds (70,3kg)