“The amount of withholding tax on income payments other than employment income is usually a fixed percentage”
http://en.wikipedia.org/wiki/Withholding_tax

“with respect to withholding tax on income that is derived by a non-resident”
http://www.revenue.ie/en/practitioner/law/double/australia.h...

“PAYE is a withholding tax on income payments to employees.”
http://www.globemploy.com/ca/pages/employer-payroll-deductio...