Usury is a sum paid for the use of money, hence interest; not, as in the modern sense, exorbitant interest.
The Jews were forbidden to exact usury (Leviticus 25:36-37), only, however, in their dealings with each other (Deuteronomy 23:19, 20). The violation of this law was viewed as a great crime (Psalm 15:5; Proverbs 28:8; Jeremiah 15:10). After the Return, and later, this law was much neglected (Neh. 5:7, 10).