What is a covenant?

Answer From The Annual Reading Schedule - Week 4 Notes For Genesis: The phrase "made a covenant" in Genesis 15:18 is literally, "cut a covenant". The covenant is defined by the Ancient Hebrew Mechanical Translation Dictionary as:

A solemn and binding agreement between two or more parties especially for the performance of some action. Covenant is instituted through the sacrifice of a choice, fattened, animal that is cut in two pieces, and between which the parties of the covenant pass. If one party fails to meet the agreements of the covenant, then the other may do the same to them.

An example of a covenant through cutting of animals in half and agreeing parties going between is shown in Genesis 15:9-10, 17-18, and Jeremiah 34:17-20.

While that is the literal example of covenants, generally speaking, it seems that covenants involve blood. Covenants between a man and wife involve the blood that results from the first time the woman lies with a man (Deuteronomy 22:15-17). There is, also, the blood of the New Covenant which is Yahushua's (Matthew 26:28, Mark 14:24, Luke 22:20, 1 Corinthians 11:25, Hebrews 12:24).