Definition
A takeoff begun from the point where a taxiway meets the runway, rather than from the runway's full-length departure end. The aircraft uses only the portion of runway remaining beyond that intersection.
Plain English
Starting your takeoff roll partway down the runway, at a taxiway entry point, instead of using the full length of the runway from the very beginning.
Context Anchor
You may hear or request this in departure instructions before takeoff, especially when a tower clears an aircraft onto the runway from a named taxiway intersection.
Derivation
Intersection here means the point where two paths cross — in this case, where a taxiway joins the runway. The takeoff begins at that crossing point rather than at the runway's start.
Why Pilots Care
The shorter runway distance must be accounted for in performance calculations to ensure the aircraft can meet required takeoff and climb gradients with adequate safety margins.
Intuition Check
Do not assume an intersection takeoff gives you the full runway. It starts where you enter the runway, so the usable takeoff distance is only the runway remaining ahead.
Example Sentence 1
Tower offered an intersection takeoff from Taxiway B, but the pilot requested full length to use all available runway.
Example Sentence 2
Before accepting the intersection takeoff the crew checked the remaining runway distance against the aircraft performance chart.