A luncheon is a formal or semi-formal midday meal, fancier than an ordinary lunch. When your school hosts a luncheon to honor award winners, everyone dresses nicely and the meal feels more ceremonial than eating in the cafeteria. Business people might attend a luncheon to network with colleagues, or a community group might hold a fundraising luncheon with speeches and special presentations.

The word carries a sense of occasion: you wouldn't call a peanut butter sandwich eaten at your desk a luncheon. A luncheon usually involves multiple people gathering together, often with a purpose beyond just eating. Hotels and restaurants offer luncheon menus for events like wedding showers, retirement celebrations, or charity gatherings.

While lunch works perfectly well for everyday meals, luncheon signals something more special and organized. Your grandmother might invite friends to a luncheon in her dining room with nice dishes and cloth napkins, while you'd just have lunch with your friends at the park. The word feels a bit old-fashioned, which is part of why people use it: it makes the meal sound more elegant and important.