Standard gauge refers to the distance between the rails on a railway track, which is set at 4 feet 8.5 inches (1,435 mm). This measurement is the most widely used gauge in the world, facilitating interoperability between different railway systems and allowing trains to travel seamlessly across regions. The adoption of standard gauge began in the early 19th century, primarily due to its efficiency and stability. Many countries, including the United States and those in Europe, have built their rail networks using this gauge, making it a crucial standard in the global railway industry.