Henotheism refers to the worship of a single god while accepting the existence of multiple gods, some of which may also be worthy of worship. In fact, the god chosen for worship may actually change depending on the circumstances.
Henotheism differs from polytheism, however, in that the latter generally involves active worship of multiple gods, whereas the former may involve a somewhat agnostic stance on whether the other gods are worthy of worship.
Henotheism also differs from monolatry, the worship of one god among others who are not considered worthy of worship.
Henotheism in Christianity
Some scholars believe that the Old Testament contains examples of henotheism that have been mistranslated or misinterpreted to combine multiple gods (Yaweh, Elohim, etc.) into a single God, and to remove or obscure the divine status of other gods.
Chistianity itself is sometimes presented (by scholars) as a henotheistic system in that it exhalts "the Father, the Son and the Holy Spirit" (or Ghost); see Trinity. The Catholic notion of saints can also be seen as somewhat henotheistic.