What does "ballast" refer to in railway terminology?

In railway terminology, "ballast" refers to the gravel or stones placed under the tracks to provide stability. It plays a crucial role in ensuring that the railway ties (sleepers) remain in place and that the tracks are correctly aligned. The ballast helps absorb the weight of the trains and provides drainage, preventing water from settling under the tracks, which could lead to erosion or instability. Properly maintained ballast is essential for the safety and efficiency of train operations, as it supports the tracks and helps mitigate movements that could lead to derailments or other issues.