Roth IRAs and Roth 401k plans are similar to traditional IRAs or 401k plans with one major exception. Whereas the money invested in a traditional IRA or 401k is taxed when you withdraw it in retirement, the money invested in a Roth IRA or 401k is not. Instead, the money is taxed up front.
There are advantages to both, and which type of account your choose depends on your individual goals and position. But with all the talk about tax reform these days, it is a good idea to explore all of the options available to you before making a decision.
To learn all about Roth accounts, read this article from Forbes.