What do we call the sum of money paid to an employee upon completing a specific task?

The correct term for the sum of money paid to an employee upon completing a specific task is "commission." This is typically a payment made to salespeople based on the sales they generate. Commission serves as an incentive for employees to perform well in sales-related roles, directly linking their earnings to the results they achieve.

In contrast, a bonus is generally a one-time payment given as a reward for performance but is not necessarily tied to a specific task completion. Wages refer to the regular payment made to employees, usually on an hourly basis, for their labor over a designated time period, while salary is a fixed regular payment, typically expressed on an annual basis and not directly linked to task completion. Thus, in the context of payment specifically linked to the achievement of a task or sales, commission is the appropriate term.