A designated Roth account is a separate account under 401(k), 403(b) or governmental 457(b) plans:

  • to which designated Roth contributions are made, and
  • for which separate accounting of contributions, gains and losses is maintained.

An advantage of a designated Roth account is that you pay tax on your contributions now, but later, when you receive a qualified distribution from the account, it is tax-free. Less tax on your plan distributions could mean more money in your pocket during your retirement.

https://www.irs.gov/pub/irs-pdf/p4530.pdf