The adhān is the Islamic call to prayer. A person called a muezzin usually performs the adhān. The adhān usually happens five times a day. Originally, the muezzin would read the adhān from the minaret (tower) or front door of a mosque. Today, many mosques have loudspeakers to amplify the adhān so the muezzin does not need to stand in the minaret.
There is a second call, known as iqama (set up) that is used to tell Muslims to line up for the start of prayers. Sunni and Shi’a Muslims use slightly different versions of the adhān.
Text adapted from Simple English Wikipedia, Creative Commons Attribution-ShareAlike License 4.0.