Ma'anar ƙamus na "kuɗin tushe" yana nufin ainihin ƙimar riba da babban bankin kasa ya kafa, wanda ake amfani da shi azaman ma'auni don sauran ƙimar riba a cikin tattalin arziki. Hakanan ana kiranta da "fararen kuɗi" ko "ƙididdigar ƙididdiga" kuma yawanci bankunan da sauran cibiyoyin kuɗi suna amfani da su azaman ginshiƙi don saita ƙimar lamuni da lamuni. Ƙididdigar ƙididdiga wani muhimmin kayan aiki ne da bankunan tsakiya ke amfani da su don magance hauhawar farashin kayayyaki da haɓaka haɓakar tattalin arziki.