Full Faith and Credit

Full faith and credit is the United States' guarantee to pay all interest and principal on every bond that the government issues.

The U.S. can make this guarantee because it can tax its people more or crank up the printing presses to Warp Factor 8 and literally print money to pay everybody back. Note that there's no guarantee that the money would actually be worth anything; you're only assured that you'll get pieces of paper in full payment of the obligation.

Find other enlightening terms in Shmoop Finance Genius Bar(f)