Manpower is the total number of people who can work to get something done. How quickly you clean your house after a big party will depend on how much manpower you've got.
The term manpower can mean "labor force," "workforce," "workers," or simply "people," and despite the man, it applies to both men and women. A large ship requires more manpower than a small sailboat, and the amount of manpower required to run Disneyland for a day is estimated to be at least 20,000 employees, most of whom aren't wearing cartoon character costumes.