Is a thrift savings plan a roth or traditional ira?

[dmertz]

Neither.  It's the federal government's equivalent of a 401(k).  The federal TSP has both traditional and Roth components.

Enter amounts shown in box 12 of your W-2 only on TurboTax's W-2 form.  Do not enter any of these amounts in the Traditional and Roth IRA Contributions section.