Réveillon is a fancy dinner party that takes place on Christmas Eve or New Year's Eve. It's a French word that means "awakening," because traditionally the meal would end in the early hours of the morning, with everyone still wide awake.
Imagine it's Christmas Eve, and you're going to a very special dinner party. Everyone is dressed up in their fanciest clothes, and the table is set with lots of delicious food. You sit down to eat and enjoy lots of different dishes - maybe some fancy cheeses and bread, roasted meats, or seafood. You might even try some special drinks that are only served at réveillon, like spiced wine or champagne.
After you've finished eating, you might sing Christmas carols, exchange gifts, or play games. You might even stay up until midnight to welcome in Christmas Day! The party atmosphere is really special, and everyone is excited to spend time together and celebrate.
Réveillon is a way to celebrate the holiday season with family and friends, and to enjoy good food and good company. It's a very special tradition, and people all over the world celebrate in their own unique ways.