The AAR Wheel Arrangement is a system used to classify the wheel configurations of locomotives and railcars. It is named after the Association of American Railroads, which developed this standard. The arrangement is denoted by a series of letters and numbers that indicate the number of axles and their configuration, such as whether they are powered or unpowered. For example, a common arrangement is 2-8-2, which means there are two leading wheels, eight driving wheels, and two trailing wheels. This system helps engineers and manufacturers communicate effectively about the design and capabilities of different rail vehicles, ensuring compatibility and efficiency in rail operations.