A shakedown is a period of testing or a trial journey undergone by a ship, aircraft or other craft and its crew before being declared operational.
For example, on May 3, 2006, Luca Badoer performed shakedowns on all three of Ferrari's Formula One cars at the Fiorano Circuit, in preparation for the European Grand Prix at the Nürburgring.
This process often incorporates an iron bird test rig in which all the flight control systems are brought together in an engineering lab, while test-articles of the physical structure will be subjected to stress and fatigue loads beyond anything the aircraft is likely to encounter in service (sometimes, although not necessarily, testing one or more articles to destruction).
Prototype aircraft are generally heavily instrumented in order to support these flight-test objectives by capturing large amounts of data for both live analysis (which on larger aircraft such as airliners may happen at dedicated flight-test engineer stations on board) and for analysis post-flight.
The ultimate aim of testing is to demonstrate the aircraft can operate safely throughout its flight envelope and that all regulatory requirements of the relevant civil aviation authorities have been met, allowing the design to receive its Certificate of Airworthiness.