Plain English Meaning
It is the lowest altitude you are allowed to fly on an airway segment if you are using GPS or WAAS to navigate. Below this altitude, the route is not guaranteed to clear terrain or to give reliable satellite-based navigation.
Full Definition
The lowest published altitude on an airway segment that guarantees both obstacle clearance and acceptable navigation signal coverage when the aircraft is navigating using GPS or WAAS. It applies only to aircraft equipped with approved GPS or WAAS receivers and is shown alongside the conventional MEA on en route low altitude charts.