There are many spellings for this spice: mahalab, mahleb, mahlebi, mahlepi, and mahaleb. Traditionally used in Greek Easter bread and mamool (a Middle Eastern cookie), this spice is common in Eastern Mediterranean and Middle Eastern cuisine.
Mahlab is the pit of the wild black cherry. It has a floral, almost rose-like, flavor combined with a subtle almond nuttiness. These seeds can easily be ground, using either a spice grinder or mortar and pestle. As there is a potential for bitterness, use it sparingly: 1/2 to 1 teaspoon of mahlab to 2 cups of flour.