A mosque, or masjid, is a general term used to describe a location where Muslims meet for prayer. The only common feature of a mosque is that it should have some indication to the qibla direction, usually a mihrab, to show the direction of prayer. The Wall Mosque is just a gray masonry prayer platform with a qibla wall at the western end that contains a large central niche that has a three-centered arched opening at each side. This prayer platform is about four feet high with a small cenotaph at the southeastern corner. There is a small entrance in line with the cenotaph on the eastern wall of the prayer platform that allows access to a space inside the platform that could be assumed to be a crypt.
More specifically, the Wall Mosque is considered an idgah. An idgah is a mosque that is generally only used on special occasions, in particular, Id prayers.2
1. Aga Khan Historic Cities Programme, Revitalization of the Gardens of Emperor Humayun's Tomb (Geneva: Aga Khan Trust for Culture and Nizamuddin Urban Renewal Initiative, 2003), 7.
2. Catherine B. Asher, Architecture of Mughal India (Cambridge: Cambridge University Press, 1992), xxvi.
Burton-Page, John. Handbook of Oriental Studies. Vol. 20, Indian Islamic Architecture: Forms and Typologies, Sites and Monuments. Leiden; Boston: Brill, 2008.