The term "computer", in use from the early 17th century (the first known written reference dates from 1613), meant "one who computes": a person performing mathematical calculations, before electronic computers became commercially available.
"The human computer is supposed to be following fixed rules; he has no authority to deviate from them in any detail." (Turing, 1950)
Teams of people were frequently used to undertake long and often tedious calculations; the work was divided so that this could be done in parallel.
The first time the term "Computer" appeared in The New York Times was February 3, 1853; an obituary stated:
Since the end of the 20th century, the term "human computer" has also been applied to individuals with prodigious powers of mental arithmetic, also known as mental calculators.
Origins in astronomy
The approach was taken for astronomical and other complex calculations. Perhaps the first example of organized human computing was by the Frenchman Alexis Claude Clairaut (1713–1765), when he divided the computation to determine timing of the return of Halley's Comet with two colleagues, Joseph Lalande and Nicole-Reine Lepaute.