A Marathon, for those of you without legs, is any long distance race.
Marathonsare typically 26 miles or more, and are considered a race. These events are in commemoration of the "Fabled run of the Greek soldier Pheidippides" who was supposed to be this soldier who ran his ass off to the ancient city of Athens to deliver a message of victory to whoever the hell was in charge of the empire at the time.
These days, Marathon runners are typically assholes who train for any given length to run 26 miles or more for whatever purpose they're trying to serve. It's like, running for the fun of it. What fun? Fitness of course!
All that's left to say is that there are Man vs. Horse Marathons, where runners compete against horses to the finish line. Isn't that sweet? Marathons.