From Longman Business Dictionary
mountainmoun·tain /ˈmaʊntənˈmaʊntn/ noun [countableC] butter/beef/ grain etc mountainECONOMICS a very large amount of food that is stored, especially by the EUROPEAN UNION, in order to prevent prices from becoming lowerThere are frequent butter, grain, wine and beef mountains which are stored at great cost or sold off cheaply to other countries.
→ see also cash mountain