I'm with tombthumb somewhat, the correct definition of Enduro lieshere an event where there are traditionally four elements of a riders ability on test, cross country riding skills, reliability of the bike and mechanic skills, maintaining a scheduled time to progress around the course with the aim to neither ride to fast or slow, and finally one or two specific sections timed to see who can be the quickest and penalise everyone else by how much slower they were than the winner.
The American name was churned up in the mid 70's by Jack Penton, Malcolm Smith and a few others who wanted to rename a traditional European Motorcycle sport of Timed, Reliability and Observation Trials for US Consumption. The American enduro rules used only by the yanks make for a far more challenging event than the international FIM based ones used in Europe which allows the rider to ride as quick as they can and to slow up and stop as they approach the check and only needing the skills required to ride a bike with a nailed open throttle. In the US riders have to maintain an average pace, secret checks are placed in hidden locations and any riders who have picked up too much speed and gained time will loose points if they ride into the check ahead of their scheduled arrival
Specialized purloined the name for an illustrious range of bikes and ever since opportunist event promoters have misused the name to mostly associate an event that is little more than a long distance XC race (Marathon) or a non competitive XC hack and to draw in fools to be parted from their money. I think the Original definition of enduro is ideal and anyone wanting to run anything different should call it by some other name to avoid confusing those who do know the difference, I would suspect the word Endurothon might well be unused at present.
I hope one day somebody out there will bring to mountain biking the joy of check cards, burning the check and special tests. Indeed someone may be organising something along this line very shortly and might be letting you know very soon. 😉