The "El" train is a common shorthand for an Elevated Railway. While many cities have used the term, it is most iconically associated with Chicago's "L" system and the Philadelphia "El". In Chicago, the system is officially designated as the 'L' (using the single letter), while in Philadelphia, the Market-Frankford Line is colloquially known as the "El." The name originates from the late 19th century when these trains were built on raised iron or steel structures above city streets to avoid the congestion of horse-drawn carriages and pedestrians. Even though parts of these modern systems now run underground (subway) or at grade level, the "Elevated" heritage remains so central to their identity that the abbreviated names have become the permanent, official brand for these rapid transit networks.