coin return slot; change slot
Refers to the opening on vending machines, ticket machines, or similar devices where returned coins or change come out.
Please don't forget to take your change from the vending machine's coin return slot.
Compound of 返金 (へんきん, 'refund' or 'returned money') and 口 (ぐち, 'opening' or 'mouth'). The reading ぐち is a rendaku form of くち.