A cooler, portable ice chest, ice box, cool box, chilly bin (in New Zealand), or esky (Australia) is an insulated box used to keep food or drink cool.
Ice cubes are most commonly placed in it to help the contents inside stay cool. Ice packs are sometimes used, as they either contain the melting water inside, or have a gel sealed inside that stays cold longer than plain ice (absorbing heat as it changes phase).
Coolers are often taken on picnics, and on vacation or holiday. Where summers are hot, they may also be used just for getting cold groceries home from the store, such as keeping ice cream from melting in a hot automobile. Even without adding ice, this can be helpful, particularly if the trip home will be lengthy. Some coolers have built-in cupholders in the lid.

They are usually made with interior and exterior shells of plastic, with a hard foam in between. They come in sizes from small personal ones to large family ones with wheels. Disposable ones are made solely from polystyrene foam (such as is a disposable coffee cup) about 2 cm or one inch thick. Most reusable ones have molded-in handles; a few have shoulder straps. The cooler has developed from just a means of keeping beverages cold into a mode of transportation with the ride-on cooler. A thermal bag or cooler bag is very similar in concept, but typically smaller and not rigid.