1. Person(s) who have previously held a position or currently hold the same position for a longer period than the newest member of a political body. Therefore an Outcumbent may still be an 'incumbent (as defined by websters/oxford english dictionaries)' as well, just with more experience than the newest incumbent. An Outcumbent is not simply a challenger to one who currently holds an office or political position (an incumbent), that is just a challenger.
Incumbent is defined by Ambrose Bierce in the devil's dictionary as "n. A person of the liveliest interest to the outcumbents."