Manpower is the number of workers available for a job. A shortage of manpower, manpower planning, insufficient manpower.
It is dated for that reason and staffing or workforce has largely replaced it in careful writing. As a unit it also once meant the physical work one person could do, which is where the word begins.
1nounmanpowerThe number of workers available for a job.
“The hospital doesn't have the manpower to keep every ward open at night.”
manpower is a labour.
Man plus power, first as a measure of the work one person could do.
From man + power.
Etymology from Wiktionary, CC BY-SA