Define the term 'gauge' in railway terminology.

In railway terminology, 'gauge' refers to the distance between the inner sides of two parallel tracks. This measurement is crucial because it affects the stability, safety, and compatibility of rail vehicles traveling on those tracks. Different gauges can lead to operational challenges, such as the need for specialized rolling stock or the adjustment of infrastructure when trains shift between different rail systems.

Understanding gauge is fundamental for ensuring proper train operations and maintaining safety standards across various railway networks. In contrast, other definitions reflect different aspects of railway operations and engineering, but they do not accurately define the term 'gauge.' For instance, weight capacity or rail segment length pertains to different characteristics of rail systems, while the height of the railway is a matter of clearance and construction rather than track spacing.