The term TRAINED FOR A MARATHON can be summarized by the solution RAN, which is a 3 letter word. This means that the person has trained for a marathon by running, which is an intense form of exercise that requires dedication and perseverance. Marathon running is a popular sport that involves running long distances, usually 26.2 miles or 42.2 kilometers. Training for a marathon requires a lot of preparation and practice, as it is a physically demanding activity.