The Yamaha XSR 155 stands for 'X-Sport Racing', which is a designation given to Yamaha's sporty motorcycles. The XSR 155 is a lightweight, easy-to-handle, and reliable bike that is great for both experienced and novice riders. It has a 155cc, liquid-cooled, single-cylinder, four-stroke engine and a six-speed gearbox. It is also equipped with an adjustable inverted fork, a lightweight aluminum swingarm, and a lightweight aluminum frame. The XSR 155 is a great choice for those looking for an affordable, sporty, and reliable bike.