A train derailment occurs when a train leaves its tracks, which can happen due to various reasons such as track defects, equipment failure, or obstacles on the tracks. This can lead to accidents that may cause damage to the train, cargo, and surrounding areas, as well as potential injuries to passengers and crew. Preventive measures, such as regular maintenance of railway tracks and train equipment, are essential to minimize the risk of derailments. Additionally, safety regulations and monitoring systems are in place to detect issues before they lead to accidents, ensuring safer travel for everyone involved.