「昼ご飯」 (hirugohan) means "lunch." It refers to the midday meal, typically eaten around noon. You use this phrase to talk about what you eat during the day. For example, 「お昼ご飯は何を食べましたか？」 (What did you eat for lunch?)

昼(ひる)間(ま)に食(た)べる食(しょく)事(じ)のことです。ランチとも言(い)います。