Commission is a stated percentage an employee receives for business or service they provide. Example a sales person that works outside the office may have a annual salary. In addition to the fixed salary they may earn a bonus or commissions for sales in excess of their sales goal. The commission is considered to be payments for the hours worked and must be included in determining the regular hourly rate. This is weather the commission is the only source of compensation or is paid in addition to salary or hourly rate. We have provided you a link for more IRS ruling on commissions pay and withholding.