The Qur'an prohibits "riba", which literally means "increase". Technically "riba" is the increase when liquid or fungible assets (cash, debt, grains, etc.) are exchanged other than at par value. The most prevalent example in today's economy is lending money at interest, for example an exchange of $100 cash now for $110 payable in a year's time, an increase of $10 (some Muslims dispute whether there is a consensus that interest is equivalent to "riba"). Investment in businesses that provide goods or services considered contrary to Islamic principles (e.g. pork or alcohol) is also "haraam" ("restricted, or excluded").