A deferral contribution is money you choose to set aside from your paycheck and put into a retirement plan, like a 401k, before you get paid. Instead of receiving that money as part of your take-home pay, it goes directly into your retirement account. This can help lower your taxable income for the year if the contribution is made on a pre-tax basis. Some plans also offer a Roth option, where you pay taxes now but your savings grow tax-free. Deferral contributions are often the main way employees build up their retirement savings over time.