What is the term for the longitudinal movement of the rails in a track?

The term for the longitudinal movement of the rails in a track is "creeping." This phenomenon occurs due to variations in temperature, where thermal expansion causes the rails to expand and contract. As the rails expand, they can move longitudinally along the track, which can lead to misalignment and potential safety issues if not properly managed. Rail systems are designed with specific tolerances and measures, such as expansion joints, to accommodate this movement and help prevent disturbances in the rail alignment that could affect train operations. Understanding creeping is essential for maintaining railway infrastructure and ensuring safe and efficient train travel.