Short answers, pulled from the story.
Monolatry is the belief in the existence of many gods combined with the insistence on worshipping only one chosen deity. Monotheism asserts that only one god exists, while monolatry accepts that other gods exist but withholds worship from all but one. Henotheism accepts both the existence of other gods and the validity of worshipping them.
Akhenaten, originally enthroned as Amenhotep IV, was a pharaoh of ancient Egypt's Eighteenth Dynasty who elevated the solar deity Aten to supreme status beginning around 1348-1346 BCE. He declared himself the sole intermediary between Aten and the Egyptian people, banned idols, built a new capital called Akhetaten at modern Amarna, and composed prayers to Aten including the Great Hymn to the Aten. Most scholars classify his religion as monolatry rather than monotheism because he never actively denied the existence of other gods.
Exodus 20:3 instructs the Israelites to have no other gods before Yahweh. Some scholars argue the phrase before me implies that other gods may exist and may be respected as long as they are ranked below Yahweh, which would suggest monolatry rather than strict monotheism.
Some historians argue that before the Babylonian captivity in the 6th century BCE, many Israelites worshipped foreign gods and idols alongside or instead of Yahweh. The books of Hosea and Nahum, among the oldest in the Hebrew Bible, record competition in the 8th century BCE between Yahwistic worship and cults the Yahwist faction called Baals, suggesting monotheism was not yet universal.
The term monolatry was possibly first used by Julius Wellhausen, the biblical scholar whose work examined the development of Israelite religion.
The classification of Mormonism as monolatrous is strongly disputed among Latter-day Saints. The LDS Church teaches that God the Father, Jesus Christ, and the Holy Ghost are three distinct beings forming one Godhead, and that prayer goes to God the Father alone. The academic framing of LDS theology as monolatrous was advanced primarily through the works of theologian Blake Ostler.