Definition:Prosthaphaeresis

Definition
Prosthaphaeresis is the process whereby multiplication and division are performed by:
 * $(1): \quad$ converting the numbers into a form where they can be added or subtracted
 * $(2): \quad$ performing the addition or subtraction
 * $(3): \quad$ converting the result back again, using the inverse process to step $(1)$.

Also known as
Some sources spell the word prosthapheiresis.

prefers the prosthaphaeresis spelling, purely because it appeasr to be more common.