From Destinypedia, the Destiny wiki
Supers are the various abilities that Guardians are able to use according to their subclass. Manifestations of the Traveler's arcane power, the Guardians channel this power to attack or defend against the many threats to the City. Examples are the Hunter's Golden Gun, the Warlock's Nova Bomb, and the Titan's Fist of Havoc.
Players have a "Super meter" above their weapon icons; when its full, the player can cast their super. The meter can be filled in four ways:
Once the player's meter is filled, it turns yellow, and the text "Super Charged" appears in the middle of the screen.
Subclass Supers (Destiny)
Subclass Supers (Destiny 2)
List of appearances