A ‘rebuilt engine’ is an engine that has been overhauled using new and used parts to new limits by the manufacturer or an entity approved by the manufacturer. The engine’s previous operating history is eradicated and it comes with zero hours total time in service, even though the engine may have had used components installed that have many hours of previous operating history. Production rebuilders or marketing material sometimes use the word ‘remanufactured’ to describe these engines.
Source: Wikipedia