Definition
A preplanned instrument flight rules (IFR) procedure published for pilots to use after takeoff from an airport. A DP provides obstacle clearance from the runway to the en route structure, and may also be designed to organize traffic flow out of busy airspace. There are two types: Obstacle Departure Procedures (ODPs), which exist solely for terrain and obstacle avoidance, and Standard Instrument Departures (SIDs), which are issued primarily for ATC traffic management and almost always require an ATC clearance.
Plain English
A published set of instructions telling an IFR pilot exactly how to climb and turn after takeoff so the airplane stays clear of terrain, towers, and other traffic on its way up to its cruising route.
Context Anchor
You see DPs during instrument flight planning, in takeoff briefings, on charts, and in clearances for flights departing an airport under instrument flight rules.
Derivation
Departure comes from the Latin partire, meaning 'to part' or 'separate' — the act of leaving a place. Procedure comes from the Latin procedere, 'to go forward.' Together, a departure procedure is literally a 'going-forward-from' set of steps — a defined path for leaving the airport safely.
Why Pilots Care
It guarantees safe obstacle clearance and a predictable path into the airway system when visibility is low.
Intuition Check
A departure procedure is not just a general takeoff plan. In instrument flying, it is a specific published or assigned path that must be followed as briefed and cleared.
Example Sentence 1
Before takeoff from a mountainous airport, the pilot reviewed the obstacle departure procedure to make sure the airplane could meet the required climb gradient.
Example Sentence 2
Following the published DP kept the aircraft clear of terrain during the climb.