The word was linguistically used by the Arabs prior to Islam to refer to an increase. In commercial practice, it referred to the increase on loans, namely, interest.

The definition of "riba" in classical Islamic jurisprudence was "surplus value without counterpart." When currencies of base metal were first introduced in the Islamic world, paying a debt in a higher number of units of this "fiat" money was not considered "riba"; jurists were concerned with the real value of money (determined by weight only) rather than its numerical value. For example, it was acceptable for a loan of 1000 gold dinars to be paid back as 1050 dinars of equal aggregate weight of gold (the value in terms of weight had to be same because all makes of coins did not carry exactly similar weight), therefore having the same real value.

రిబా నిషేధం
ఖురాన్
ఖురాను, హదీసుల మూలాలు
పద వ్యుత్పత్తి