diners
n. plural-only B1 Intermediate US //ˈdaɪnɝz// UK //dˈaɪnəz// din·ers
n. people who are eating a meal, usually in a restaurant.
n. individuals consuming a meal, specifically within the context of a commercial dining establishment.
The restaurant was full of happy diners.
Waiters moved quickly between the tables to ensure all diners received their drinks before the main course arrived.
The establishment caters to discerning diners who expect locally sourced ingredients and an extensive wine list to accompany their multi-course tasting menu.
Usage
While 'diner' refers to an individual or a type of casual restaurant, the plural form 'diners' most frequently identifies the collective group of customers in any eatery.