Sansho is a Japanese spice made by grinding the dried leaves of the Japanese Prickly Ash (aka Szechuan Peppercorn) tree.
It also applies to the actual Szechuan Peppercorns when ground. Most Szechuan Peppercorns are sold already ground in Japan.
The leaves have a bit of a citrus-fruit aroma, and a milder pepper taste than the berries (aka Szechuan Peppercorns) do.
Sansho means “wild pepper”. It’s derived from one of the Chinese names, “shan jiao”.