to do extensive work on something, performing repairs and/or building it again from a damaged or destroyed state;
e.g. They are planning to rebuild the hotel that was damaged in the fire.
(verb)
to change something extensively, often to return it to a previously-held state;
e.g. They decided to rebuild the educational system to benefit students.
(noun)
an instance of making extensive repairs or changes to something and/or building it again, or something that has been thus repaired or built, especially a machine or vehicle;
e.g. They have almost finished their rebuild of the vintage car.