Original: A mihrab (maharib) is semicircular niche in the wall of a mosque that indicates the qibla; that is, the direction of the Kaaba in Mecca and hence the direction that Muslims should face when praying.
Simplified: The Mihrab 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).