Sumac is a very popular spice in Middle Eastern and certain Mediterranean cuisines. The berries of the Sumac bush are dried then ground to form a deep red, almost purplish coarse powder.
It is sour, tangy, lemony with just a hint of pepper. You could have lots of fun using it in your kitchen in place of lemon juice, tamarind and even vinegar.
Substitute: lemon juice and zest.
Lots of recipes on this site use sumac, like:
Coban Salatasi (Turkish Shepherd Salad)