A gravity bomb is a weapon, which, when released by an aircraft, moves to its point of impact only through gravitation; it has no rocket booster or any supplementary active propulsion. Most bombs have fins or other aerodynamic control surfaces, if for no other reason than to stabilize the trajectory. "Dumb bombs" use aerodynamic surface only for stabilization; they have no navigational or target-seeking capability.
Some gravity bombs may have small wings or other aerodynamic surfaces that extend range through aerodynamic lift. As long as there is no supplementary propulsion, a gravity bomb may have a significant range increase from aerodynamic forces; see, for example, the AGM-154 Joint Standoff Weapon (JSOW). They may use aerodynamic forces to become a guided bomb, such as the Joint Direct Attack Munition (JDAM).
Gravity bombs can have any type of payload, including nuclear (e.g., B61, conventional high explosive (e.g., Mark 8x series conventional bomb), incendiary, propaganda leaflets, or even an inert filler such as concrete. Inert fillers may be used for training, or, with guided bombs of sufficient accuracy, destroy a target through the pure kinetic energy of the gravity-accelerated mass of the bomb.
Payloads may be unitary, meaning there is a single mass of explosive or incendiary material. Cluster bombs contain multiple submunitions, which can have the same or different payloads.
Bombs can have a reinforced case so that they can penetrate earth, concrete, or armor. Alternatively, a bomb with a unitary filler can have a thin case to maximize the payload; such a bomb may have a fuze that detonates it in the air, or certainly on contact with a hard surface.