semicircular niche in the wall of a mosque that indicates the qibla

The Mihrab (Arabic: محراب pl. محاريب) is a niche in the wall of a mosque. It indicates the qibla (the direction of the Kaaba in Mecca, the direction that Muslims should face when praying). The wall in which a mihrab appears is the "qibla wall."

Mihrab and Minbar in the Great Mosque in Aleppo, Syria