Riba refers to interest or usury which is forbidden in Islamic economic jurisprudence. There are two main types of riba - riba al-nasiah which refers to time period and riba al-fadl which is the exchange of commodities of the same kind in unequal proportions. Scholars have different views on what constitutes riba al-fadl based on characteristics of commodities. Riba is prohibited in Islam as it is an unlawful forced addition while profit from trade and business is permitted if derived fairly through mutual consent and sharing of risk.