The word "Riba" means excess, increase or addition, which according to Shariah terminology, implies any excess compensation without due consideration (consideration does not include time value of money). The definition of riba in classical Islamic jurisprudence was "surplus value without counterpart", or "to ensure equivalency in real value", and that "numerical value was immaterial."
Applying interest was acceptable under some circumstances. Currencies that were based on guarantees by a government to honor the stated value (i.e. fiat currency) or based on other materials such as paper or base metals were allowed to have interest applied to them.^[9] When base metal currencies were first introduced in the Islamic world, the question of "paying a debt in a higher number of units of this fiat money being riba" was not relevant as the jurists only needed to be concerned with the real value of money (determined by weight only) rather than the 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 (i.e., the value in terms of weight had to be same because all makes of coins did not carry exactly similar weight).