What is the meaning of Rigid?

Stiff, rather than flexible.

Fixed, rather than moving.

Rigorous and unbending.

Uncompromising.

An airship whose shape is maintained solely by an internal and/or external rigid structural framework, without using internal gas pressure to stiffen the vehicle (the lifting gas is at atmospheric pressure); typically also equipped with multiple redundant gasbags, unlike other types of airship.

A bicycle with no suspension system.

to stretch, to distend

to rule, direct

rigid

Source: wiktionary.org