[Army Air Corps]

According to most definitions, the words are distinguished as follows:

Dirigible: manoeuverable lighter-than-air craft; steerable airship.
Blimp: non-rigid dirigible.
Zeppelin: Rigid dirigible. Also acceptable to use the term Rigid Airship.

Supporting sources: The National Air and Space Museum, Graf Zeppelin & Hindenburg:The Golden Age of the Great Passenger Airships, Dictionary of Aviation, etc...

[jamaksin]

Also see:

Airshipwreck, Len Deighton and Arnold Schwartzman Jonathan Cape Limited, 30 Bedford Square, London, WC1 ISBN 0-224-01384-X, First Published 1978

United States Naval Air Station Lakehurst, NJ "The Hindenburg Memorial"

Distinction is made ... rigid versus non-rigid in both above.

Regarding "manoeuverable" ... FAA rules on "right-of-way" ... ballons highest as it is ain't got none! At the mercy of the winds ... of course ballast helps.