An airship is a lighter than air aircraft. An airship has a huge main body that contains lighter than air gas. The gas raises the aircraft and keeps it afloat the same way a gas balloon is lifted. But airships, unlike balloons have engines to move them thorough the air and almost always have equipment for steering. Balloons are moved by wind and can't be steered, they travel in the direction the wind takes them. Airships are also different to helicopters and aeroplanes which are heavier than air. Also unlike airships they use their engines, rotor blades and wings etc. to keep them afloat.
Airships were introduced in the 1800's as the first manned flying machines capable of prolonged flight and steering. In World War One ( 1914 - 1918 ), airships were used as bombers, for protecting ships against submarine attack and for other things. Before and after the war they were used to carry passengers.
Airship passenger services reached their peak in the 1930's but a series of disastrous crashes and the increasing popularity of airplanes brought airship passenger services to an end. Today. Many countries have renewed their interest in airships for use for such things as surveillance, offshore patrols, lifting bulky cargoes and advertising.