Mason jars are glass containers commonly used for preserving food. They come in various sizes and have a two-part lid system, which includes a flat metal disc and a screw-on band. This design creates a vacuum seal that helps keep food fresh for long periods, making them popular for canning fruits, vegetables, and jams. In addition to food preservation, Mason jars are often used for crafts, storage, and decoration. They can hold items like spices, buttons, or even serve as vases. Their versatility and rustic charm have made them a favorite in homes and kitchens.