on demand
From Longman Dictionary of Contemporary Englishon demandon demandformalASK FOR something/ASK somebody TO DO something whenever someone asks Should you feed your baby on demand, or stick to a timetable? → demandFrom Longman Business DictionaryRelated topics: Financeon demandon deˈmand adverb American English FINANCE if money is lent on demand, it must be repaid immediately if the lender asks for itSYNAT CALL, ON CALL BrE