A dirigible, also known as an airship, is a type of lighter-than-air aircraft that can be steered and controlled. It consists of a large gas-filled envelope, typically filled with helium or hydrogen, which provides lift. Dirigibles are equipped with a propulsion system, allowing them to navigate through the air. They are often used for advertising, surveillance, and tourism. Historically, dirigibles gained popularity in the early 20th century, with notable examples like the Hindenburg and Zeppelin. Although they were once a common mode of air travel, safety concerns and the rise of airplanes led to a decline in their use. Today, they are primarily used for specialized purposes.