From Longman Business Dictionary
counterfoilcoun·ter·foil /ˈkaʊntəfɔɪl-tər-/ noun [countableC] British EnglishBrEBANKING the part of something such as a cheque that you complete and keep as a record of how much you have spentSYN CHEQUE STUBI enclose the ticket counterfoil as proof of purchase.