In the Bible a "covenant" is a formal binding agreement, most often between God and a person or people, marked by promises and a sign; one of the earliest is the covenant God makes with Abraham in Genesis 17.
Genesis 17:7 in the King James Version reads:
And I will establish my covenant between me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee.
The verse appears in Genesis 17, in the passage where God establishes his covenant with Abraham. Read it in context at Genesis 17:7, or the full chapter at Genesis 17. Encyclopedia entry: en.wikipedia.org/wiki/Covenant_(biblical).