Definition
An external fuel tank attached to an aircraft that is designed to be jettisoned (released and dropped away) in flight when empty or when the aircraft needs to reduce weight and drag. Drop tanks extend the range of an aircraft by carrying additional fuel beyond what the internal tanks can hold, and are most commonly used on military aircraft.
Plain English
An extra fuel tank hung on the outside of an aircraft that can be released and dropped off in flight once it's no longer needed, usually after its fuel has been used.
Context Anchor
Seen mostly in military aircraft, special-purpose aircraft, and aircraft performance or fuel-range discussions.
Derivation
Called a 'drop' tank because the tank is literally dropped from the aircraft once empty, shedding the weight and drag it creates.
Why Pilots Care
Jettisoning an empty drop tank extends range on the outbound leg while restoring better climb, speed, and handling once the extra weight and drag are removed.
Intuition Check
A drop tank is not a normal built-in fuel tank. It is an outside tank made to be released from the aircraft when needed.
Example Sentence 1
The fighter carried two drop tanks under its wings to extend its range on the long overwater flight.
Example Sentence 2
During the emergency climb, the pilot jettisoned the empty drop tanks to reduce drag and improve performance.