A patron, a client; one who purchases or receives a product or service from a business or merchant, or intends to do so.
"The server smiled warmly at every customer as they waited for their orders in the bustling restaurant."
In plain English: A customer is someone who buys goods or services from a business.
"The customer was very polite when he asked for help finding his size."
Usage: Use "customer" to refer specifically to someone who buys goods or services from a particular business, such as a shopper at a store or diner at a restaurant. Do not use it interchangeably with "client," which typically implies a professional relationship involving ongoing advice or specialized services.
The word customer originated in Medieval Latin as custumarius, meaning a toll-gatherer or tax-collector. It traveled into English through Old French and Middle English before evolving to refer simply to someone who buys goods.