Final answer:
The decorated niche that faces Mecca in an Islamic mosque, representing the direction of prayer, is known as the mihrab.
Step-by-step explanation:
In the Islamic mosque, the decorated niche that faces Mecca and represents the direction of prayer is termed the mihrab. The mihrab is a semicircular niche in the qibla wall—that is the wall inside a mosque which faces the Kaaba in Mecca. When observing the interior architecture of a mosque, one would find that the mihrab is usually the most ornate feature owing to its significance in Islamic ritual, marking the direction that all Muslims face during prayer. In general, a mosque may have other features such as a minaret, from which the call to prayer is announced, but it is specifically the mihrab that directly relates to and indicates prayer direction.