Riba (Arabic: ربا ,الربا، الربٰوة, ribā or al-ribā, IPA: [ˈrɪbæː]) is an Arabic word used in Islamic law and roughly translated as "usury": unjust, exploitative gains made in trade or business (especially banking). Riba is mentioned and condemned in several different verses in the Qur'an (3:130, 4:161, 30:39, and the commonly referenced 2:275-2:280). It is also mentioned in many hadith (reports of the life of Muhammad).
While Muslims agree that riba is prohibited, not all agree on what precisely it is (its definition). The term is often used to refer to interest charged on loans, and the widespread belief among Muslims that all loan or bank interest is riba forms the basis of the $2 trillion Islamic banking industry. However, not all Islamic scholars have equated riba with all forms of interest; nor do they agree on whether riba is a major sin or simply discouraged (makruh), or on whether it is a violation of Sharia law to be punished by humans rather than by God.