Plain English Meaning
An RNAV DP is a departure route that the aircraft flies by going from one named point in space to the next, using onboard navigation equipment instead of following signals from ground stations.
Full Definition
A published instrument departure procedure that uses area navigation (RNAV) to define the route, allowing the aircraft to fly directly between defined waypoints rather than tracking to or from ground-based navigation aids. RNAV DPs are charted as either Standard Instrument Departures (SIDs) or Obstacle Departure Procedures (ODPs) and require an aircraft equipped with suitable RNAV equipment, typically GPS or an FMS, along with appropriate authorisation.