Plain English Meaning

Taking off and flying away from the airport using outside visual references and your own eyes to stay clear of terrain and weather, then calling ATC once airborne to pick up your IFR clearance for the rest of the flight.

Full Definition

A departure conducted under Visual Flight Rules in which the pilot is responsible for terrain and obstacle clearance, even when the flight will later operate on an IFR flight plan. An IFR clearance is typically picked up airborne from ATC after departure, and the pilot must remain in visual meteorological conditions until that is received and accepted.