Yes, an Endurance event is exactly an MTB Marathon, the UCI have some rules and definitions somewhere, if you can find them on the most un-interrogatable website ever. Can be laps of a course like Mountain Mayhem (muddy fields or not) or point to point like the Merida series.
An Enduro event on the other hand will involve probably about the same distance of riding, but in a single loop, and you are only timed on the special stages, which will be mainly sections of descent.
Yes, it would be good if organisers were consistent about this !!
Was chatting to Steve at the weekend one of the Gravity series organisers about getting some rules set up for Enduros that we can all work towards, makes life easier for all.