Khalifa (خليفة ẖalīfä) is Arabic for "stewardship" of nature and family, and is a key obligation of a Muslim.

The word is most commonly used for the Islamic leader of the Ummah, which is translated into English as Caliph (see there for this definition). However there are also several other specific uses of the same title for Muslim offices at lower levels of power and authority. (Wikipedia)