a marathon race
he marathon is a long-distance running event with an official distance of 42.195 kilometres, thus 42.19500 kilometers = 42 195 meters
5 kilometers is 5000 meters, which is a bit over 26 miles or 42 kilometers. You shouldn't use the word 'marathon' to mean any long distance race.
5 meters, if it only lasts 5 seconds. 800 meters, if it lasts at least 2.5 hrs.
A marathon's distance is 42.195 km which would be 42195meters.