What does the term "ballast" refer to in railway terminology?

The term "ballast" in railway terminology specifically refers to the materials that are used to support and stabilize railroad ties and track. Ballast typically consists of crushed stone or gravel that is placed beneath and around the ties (the wooden or concrete beams that hold the rails). This material provides a stable base for the track, helps maintain the alignment of the rails, and aids in drainage to prevent water accumulation that could compromise track integrity.

In contrast, a type of train car used for transporting goods does not pertain to ballast, as it relates to rolling stock rather than track construction. The action of compressing dirt around the rails for stability describes a different maintenance procedure that might enhance the infrastructure but does not define ballast. Finally, instruments used to measure track integrity are separate tools used for maintenance and inspection and do not have a direct connection to the foundational materials that comprise the track bed.