1.
difficult to book, hard to get a reservation
Describes a restaurant, hotel, service, or event that is extremely popular and therefore very difficult to secure a reservation for. A common descriptor in restaurant reviews and travel writing.
A compound of 予約 (reservation, booking) + 困難 (difficult). Used as both a noun and a na-adjective. Extremely common in food and restaurant culture writing, especially in descriptions of exclusive or highly popular restaurants.
Often used as a compound modifier before 店/店 (restaurant/shop): 予約困難店 (a hard-to-book restaurant).