Definition
The phase of flight from the moment the airplane lifts off the runway until it reaches a safe maneuvering altitude, typically at least 500 feet above ground level, where a positive rate of climb has been established and the airplane has been configured for sustained climb (gear and flaps retracted as appropriate, climb airspeed established).
Plain English
The first part of climbing after takeoff. It begins the moment the wheels leave the ground and ends once the airplane is climbing steadily at a safe height above the ground.
Context Anchor
You encounter this term in takeoff training, especially when discussing what to do immediately after liftoff and before settling into the rest of the departure.
Derivation
Initial comes from Latin initium, meaning 'beginning.' So initial climb literally means the beginning portion of the climb -- the first segment after the airplane is airborne.
Why Pilots Care
Getting the initial climb right ensures obstacle clearance and establishes a stable flight path before the pilot makes further configuration changes.
Intuition Check
Do not read initial climb as the whole climb to cruising altitude. Here it means the first climb segment immediately after takeoff.
Example Sentence 1
After liftoff, the pilot maintained the recommended initial climb airspeed until reaching 1,000 feet above the airport.
Example Sentence 2
During the initial climb the pilot watches for obstacles while maintaining the target airspeed.