What constitutes an airship?

An airship is defined as a power-driven, lighter-than-air aircraft. This classification is based on its ability to float in the air due to the lift generated by gas, such as helium or hydrogen, which is less dense than the surrounding atmosphere. The inclusion of "power-driven" indicates that an airship is equipped with engines that allow it to navigate and control its direction, differentiating it from mere balloons.

In contrast, options that mention a fixed wing, glider aircraft, or powered jet aircraft describe different categories of aircraft. Fixed-wing aircraft rely on aerodynamics for lift through their wings and do not fall under the lighter-than-air classification. Gliders are designed for unpowered flight, often relying on thermals or other natural lift, so they also do not fit the definition of an airship. Powered jet aircraft utilize jet propulsion and are significantly heavier than air, making them distinct from lighter-than-air crafts. Thus, the correct answer focuses on the unique characteristics that define an airship in the realm of aviation.