A Solo 401k is also known as a self-employed 401k. Full-time freelancers and self-employed individuals are not able to take advantage of a permanent employer retirement plan, so instead that can opt for a solo 401k. (Which is even better!)
There is one key difference between traditional and Roth IRAs. With traditional IRA plans, you invest funds into the plan pre-tax.
This means you do not pay income or other taxes on funds the year you invest them into a traditional IRA.