The brown color imparted to the skin by exposure to the sun or open air due to training for an Ironman Triathlon. Due to long hours of training, this particular tan is denoted by many different levels of coloration in many varying patterns. Most notably:

3 or more tan lines on each arm
tan lines from wrist mounted watch or GPS
tan lines from wearing cycling gloves
3 or more tan lines on the thighs from varying shorts length
tan lines on lower legs from socks and capri length tights