Szechuan Pepper or Sichuan Pepper
Sichuan pepper, sometimes called szechuan or szechwan pepper isn't really a pepper at all. Its a small fruit that grows on a thorny bush or more correctly the prickly ash tree in Asia. Its from the zanthoxylum genus.
Sichuan pepper is used in many dishes in Asia. It has a unique lemony or citrus-like aroma. Sichuan has an odd ability, due to having a compound called sanshool that causes a "tingly sensation" to your tongue. The hulls of the berry are usually used for spice mixes such as the Chinese five spice mix. Its possible that these unique properties in sechuan might bring out the flavors or "spiciness" of the other spices.
Sichuan pepper is used in many food dishes in China, India, Japan, Indonesia and Nepal. Its sometimes referred to as Nepal Pepper. It is used as a spice for pork, chicken and duck dishes. It is also used in noodle dishes and with dumplings.
Sichuan pepper is said to also have medicinal properties, as well. In North America the bark of a similar tree of the same genus is used for toothaches. Some traditional Chinese medicinal uses are for gastrointestinal ailments, stomach pain and is used topically for skin ailments.