An expansion joint is a structural element designed to absorb movement caused by temperature changes, settling, or vibrations in buildings and bridges. These joints allow for the expansion and contraction of materials, preventing damage such as cracking or buckling. They are commonly used in concrete, metal, and piping systems. Expansion joints are typically made from flexible materials like rubber or metal and are strategically placed in areas where movement is expected. By accommodating these movements, expansion joints help maintain the integrity and longevity of structures, ensuring safety and functionality over time.