Szechuan Peppers are not technically in the pepper family, but rather a member of the Rutaceae (rue or citrus) family. The taste profile is hard to describe, but a visit to a true Szechuan style Chinese restaurant will offer you a spice taste like no other.
Szechuan pepper is characterized by its tart, lemony, acrid flavor; it is also woodsy and slightly peppery, with a complex progression of flavors that Tony Hill, in The Contemporary Encyclopedia of Herbs and Spices, describes as moving from "citrus zest to numbing shock to lingering mild sweetness."
We love Szechuan pepper and we were down to our last pinch. It is not easy to find but my brother recommended Sullivan Street. So happy we placed an order for the pepper and some other spices. Our order arrived quickly, and just in time for our dinner of mapo tofu! Thanks!