Generally, the types of railway track gauges can be divided into the standard gauge, the narrow gauge, and the broad gauge. The most common gauge is standard gauge 1435mm (4 feet 8 1/2 inches). Gauges narrower than 1435mm are called narrow gauge while wider than 1435mm are called broad gauge. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.