Normal inspection - say Annual - aircraft goes into the hangar for the full inspection and remains there for as long as it takes to complete all the inspection items - can be days/weeks/months!
Progressive inspection - must be approved - say Annual - the inspection is broken into smaller chunks which are done in stages over a period of time so that the aircraft is not out of service for such a single long period while at the same time meeting all the requirements of the required maintenance.
Regards,
DFC