FAI definition

FAI glider classes as set by the Sporting Code Section 3

3.1.2  Record classes FAI Class D records are in the following classes:
a. OPEN any FAI Class D aircraft
b. 15 METRE any FAI Class D aircraft with a wingspan not exceeding 15,000 mm
c. 13.5 METRE any FAI Class D aircraft with a wingspan not exceeding 13,500 mm
d. ULTRALIGHT any FAI Class D aircraft with a takeoff mass not exceeding 220 kg

Note: Class D aircraft = glider

For the International Aeronautical Federation, an Ultralight Glider is a glider whose takeoff weight is not above 220kg.

Here you can get the Sporting code