The Law of Elohim is a principle that Mormon men promise to obey during the endowment ceremony, which usually takes place in a temple. Mormon men promise to obey God's law, and in exchange God delivers to men the laws of obedience and sacrifice. The term is derived from Mormon teachings that "Elohim" is a name of God the Father.
Some fundamentalist sects of Mormonism teach that "Elohim" is the name of a council of gods headed by God the Father, and that Mormon men are therefore promising to obey the law of a council of gods.
References
Law of Elohim Wikipedia(Text) CC BY-SA