In the tax code, the Roth account in your 401(k) is called the "designated Roth account". Colloquially it's called a "Roth 401(k)." Similar to a Roth IRA, your contributions to the designated Roth account are made after-tax and investment growth in the account is tax free once the requirements for qualified distributions are met. This differs from the money in the traditional 401(k) account which is tax-deferred, so you'll pay taxes when you take the money out.