Alternative forms 
- a small or obscure place, especially such a restaurant
- (colloquial, chiefly UK) an automated teller machine (ATM)
Usage notes 
Although either plural can be used for both meanings, hole-in-the-walls tends to be most commonly used for the "obscure place" sense, and holes-in-the-wall is more frequently used to mean "automated teller machines".
The British sense of an automated teller machine is a trademark of Barclays.