A gala is a big party. If you're going to a gala, you'll want to wear your fanciest ball gown — you'll want to look great for the best party of the year.
A gala often features entertainment and dinner, and sometimes dancing and an auction. It's like a prom — but for adults. If you want to raise money for your favorite hospital, or museum, or theater, you could throw a gala, charge people a lot to attend, and give your profits to the charity. A gala can also be just a big celebration, like a gala dinner before the Oscars ceremony. Gala is from the Old French gale, "rejoicing."