A blimp, or non-rigid airship, is a floating airship

Airship

An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...

 without an internal supporting framework or keel. A non-rigid airship differs from a semi-rigid

Semi-rigid airship

Semi-rigid airships are airships with a partial framework. These often consist of a rigid, or occasionally, flexible, keel frame along the long axis under the aerodynamic hull envelope. The partial framework can also be located inside the hull...

 airship and a rigid airship

Rigid airship

A rigid airship is a type of airship in which the envelope retained its shape by the use of an internal structural framework rather than by being forced into shape by the pressure of the lifting gas within the envelope as used in blimps and semi-rigid airships.Rigid airships were produced and...

 (e.g., a Zeppelin

Zeppelin

A Zeppelin is a type of rigid airship pioneered by the German Count Ferdinand von Zeppelin in the early 20th century. It was based on designs he had outlined in 1874 and detailed in 1893. His plans were reviewed by committee in 1894 and patented in the United States on 14 March 1899...

) in that it does not have any rigid structure, neither a complete framework nor a partial keel, to help the airbag maintain its shape. Rather, these aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 rely on both a higher pressure of the lifting gas

Lifting gas

Because of the Archimedes' principle, a lifting gas is required for aerostats to create buoyancy. Its density is lower than that of air . Only certain lighter than air gases are suitable as lifting gases.- Hot Air :...

 (usually helium

Helium

Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

) inside the envelope and the strength of the envelope itself.

The term "blimp" refers only to free-flying aircraft.