noun
daily lunch special; today's set lunch
Common at restaurants and cafeterias, referring to a set meal that changes each day.
今日の日替わりランチは何ですか？
What is today's lunch special?
あの店の日替わりランチはいつもお得だ。
That restaurant's daily lunch special is always a good deal.
定食 is a set meal that is always on the menu, while 日替わりランチ changes daily.
Compound of 日替わり (daily change) and ランチ (lunch, from English).