prayer niche / sanctuary / chamber
Masculine noun (mifʿāl pattern). Plural: مَحَارِيبُ (maḥārīb). In the Quran, refers to a private worship chamber. In mosques today, it is the niche indicating the direction of prayer.
The miḥrāb in every mosque indicates the qiblah (direction of Makkah). Maryam's miḥrāb was her place of solitary worship where angels brought her food.