ADS B aircraft categories

A- = Unspecified powered aircraft
A1 = Light (< 15 500 lbs.)
A2 = Small (15 500 to 75 000 lbs.)
A3 = Large (75 000 to 300 000 lbs.)
A4 = High Vortex Large(aircraft such as B-757)
A5 = Heavy (> 300 000 lbs.)
A6 = High Performance ( > 5 g acceleration and > 400kts)
A7 = Rotorcraft
B- = Unspecified unpowered aircraft or UAV or spacecraft
B1 = Glider/sailplane
B2 = Lighter-than-Air
B3 = Parachutist/Skydiver
B4 = Ultralight/hang-glider/paraglider
B5 = Reserved
B6 = Unmanned Aerial Vehicle
B7 = Space/Trans-atmospheric vehicle
C- = Unspecified ground installation or vehicle
C1 = Surface Vehicle - Emergency Vehicle
C2 = Surface Vehicle - Service Vehicle
C3 = Fixed Ground or Tethered Obstruction

See also this image: https://imgur.com/a/PIQYx0W