Lunch; the meal eaten at midday. Colloquially interchangeable with 'hiru-gohan' or 'lunch'.
今日の昼飯はコンビニで買ったおにぎりだ。
Today's lunch is a rice ball I bought at the convenience store.
お腹が空いたから、昼飯を早めに食べよう。
I'm hungry, so let's eat lunch a bit early.
彼はいつも昼飯を外で済ませる。
He always eats lunch out.