Expansion joints are flexible connectors used in structures like bridges, buildings, and pipelines. They allow for movement caused by temperature changes, settling, or vibrations, preventing damage to the materials. Without these joints, materials can crack or warp due to stress. These joints are typically made from materials like rubber, metal, or plastic, designed to absorb movement. They come in various shapes and sizes, depending on the specific application. Proper installation and maintenance of expansion joints are crucial for ensuring the longevity and safety of structures, such as bridges and highways.