Definition
The angle between the airplane's longitudinal axis (the nose-to-tail centerline) and its actual track over the ground, intentionally established by turning the nose into the wind to compensate for crosswind drift so the airplane tracks straight along the desired path.
Plain English
When the wind is blowing from the side, the pilot points the nose slightly into the wind so the airplane actually moves along the line they want over the ground. The amount the nose is offset from that line is the crab angle.
Context Anchor
Used during crosswind takeoffs, after lift-off, approaches, and any time the airplane must stay on a desired path while wind is pushing it sideways.
Derivation
From the sideways walk of a crab. The airplane's nose points one way while it travels another, similar to a crab moving sideways relative to the direction it faces.
Why Pilots Care
Using the correct crab angle keeps the aircraft on the intended path and aligned with the runway in crosswinds, preventing drift that could lead to a runway excursion.
Analogy
Like aiming a boat slightly upstream when crossing a river. The bow points up-current, but the boat moves straight across.
Intuition Check
A crab angle is not the same as turning the airplane away from the runway path. The airplane is still moving along the desired path; its nose is simply pointed somewhat into the wind to cancel sideways drift.
Example Sentence 1
After lift-off, the pilot established a crab angle into the wind to keep the airplane tracking along the extended runway centerline.
Example Sentence 2
On final approach the pilot held a ten-degree crab angle until the flare, then transitioned to a sideslip for touchdown.