Non-rigid airship (blimp)

A non-rigid airship, commonly called a blimp, is a type of lighter-than-air craft that relies on the pressure of its internal gases to maintain its shape. It has no internal frame; instead, the envelope (the outer shell) contains a gas, like helium, that makes it buoyant. The shape is maintained by internal pressure; when the gas expands or contracts, the blimp can change size slightly. These airships are often used for advertising, surveillance, and entertainment because they can hover, move smoothly through the air, and are relatively easy to control.