午饭(wǔ fàn) - lunch in Mandarin

午饭 (wǔfàn) is lunch, from 午 (wǔ, "noon, midday") plus 饭 (fàn, "cooked rice, meal"). It follows the same build as 早饭 (zǎofàn, "breakfast") and 晚饭 (wǎnfàn, "dinner"), the time word stacked in front of 饭 (fàn).

吃午饭 (chī wǔfàn), "to eat lunch", is the phrase you will use most; 午 (wǔ) itself rarely stands alone in speech outside compounds like 中午 (zhōngwǔ, "noon") and 下午 (xiàwǔ, "afternoon"). As with breakfast, there is a more formal alternative, 午餐 (wǔcān), seen on menus and in writing, while 午饭 (wǔfàn) is the spoken default.

Lunch in China is often the main meal of the day for office workers, with a fixed midday break built into the working day for it, so asking 午饭吃了吗 (wǔfàn chī le ma), "have you had lunch", is as ordinary a check-in as asking about the weather.