What is the official FAA definition of the term enroute? I recently saw a ferry permit which included the following limitation:


  Flight in IMC authorized for ENROUTE operations ONLY


Great, IMC is allowed enroute!  But wait, where does the "enroute" portion of the flight start and end?  



I did some research and found the following ICAO definition for enroute:


  Instrument Flight Rules (IFR): From completion of Initial Climb
  through cruise altitude and completion of controlled descent to the
  Initial Approach Fix (IAF).
  
  Visual Flight Rules (VFR): From completion of Initial Climb through
  cruise and controlled descent to the VFR pattern altitude or 1,000
  feet above runway elevation, whichever comes first.


That seems pretty straightforward, but I was looking for something FAA specific and found this in Chapter two of the FAA's Instrument Procedures Handbook:


  The en route phase of flight is defined as that segment of flight from
  the termination point of a departure procedure to the origination
  point of an arrival procedure.


That doesn't match the ICAO definition, but it also isn't from an actual regulation or LOI either.



This leaves arrivals and departures as slightly ambiguous, and they often start high in the flight levels where it can be hard to avoid IMC, even on a nice VFR day at the airport (and also seems contrary to what they are trying to accomplish).  Are arrivals and departures considered enroute or some other phase of flight?
FAA follows the ICAO definition for describing the phases of flight.
FAA is a member of the CAST/ICAO Common Taxonomy Team that formed the Phase of Flight Definitions and Usage Notes in October 2002. From the CAST/ICAO Common Taxonomy Team site:

Federal Aviation Administration (FAA)- FAA has officially adopted the aircraft make model series (ACFT-MMS) and phase of flight taxonomies as an agency-wide data standard for its internal systems.

So, the enroute phase of flight is the same (just repeating from the same document):

Instrument Flight Rules (IFR): From completion of Initial Climb through cruise altitude and completion of controlled descent to the Initial Approach Fix (IAF).
Visual Flight Rules (VFR): From completion of Initial Climb through cruise and controlled descent to the VFR pattern altitude or 1,000 feet above runway elevation, whichever comes first.
This phase of flight includes the following subphases:
• Climb to Cruise: IFR: From completion of Initial Climb to arrival at initial assigned cruise altitude. VFR: From completion of Initial Climb to initial cruise altitude.
• Cruise: Any level flight segment after arrival at initial cruise altitude until the start of descent to the destination.
• Change of Cruise Level: Any climb or descent during cruise after the initial climb to cruise, but before descent to the destination.
• Descent: IFR: Descent from cruise to either Initial Approach Fix (IAF) or VFR pattern entry. VFR: Descent from cruise to the VFR pattern entry or 1,000 feet above the runway elevation, whichever comes first.
• Holding: Execution of a predetermined maneuver (usually an oval racetrack pattern) which keeps the aircraft within a specified airspace while awaiting further clearance. Descent during holding is also covered in this subphase.