Szechuan Pepper (sichuan peppercorns) are the brown berries of a Chinese spice, which comes from the prickly ash tree. The berry is similar to a black peppercorn but contains a tiny seed and has a distinctive flavor that is less sharp. There has been a US ban on the seeds because it may carry a citrus canker but as of 2005 the ban has been lifted. All product must be heat processed before it is allowed to enter the U.S.
If you don't have Szechuan pepper, you can use one of these substitutes (per tablespoon needed)