A credit note is a piece of paper that a shop gives you when you return goods that you have bought from it. It states that you are entitled to take goods of the same value without paying for them.
[British]regional note: in AM, use credit slip
credit note in British English
(ˈkrɛdɪt nəʊt)
noun
British
a receipt given to a customer who has returned goods to a shop which can be deducted from the cost of future purchases
▶ USAGE The abbreviation for credit note is C/Norc/n