According to the FAA:
The term heavy is used during radio transmissions between air traffic control and any aircraft which has been assigned a maximum takeoff weight (MTOW) rating of 136 tonnes (300,000 lb) or more. Such “heavy” aircraft over 136 tons create wake turbulence from the wings. Thus, the term is included in radio transmissions around airports during take off and landing, incorporated into their call sign so as to warn other aircraft that they need extra distance to avoid this wake turbulence.
Currently the only “super” aircraft are the Airbus A380 and Antonov An-225.