Definition 1 of 2
Definition
The rotation of an aircraft about its longitudinal axis, tilting the wings so that one wing is lower than the other. Bank is the maneuver used to initiate and sustain a turn, with the angle of bank measured between the aircraft's lateral axis and the horizon.
Plain English
Tilting the airplane sideways by raising one wing and lowering the other. This is what you do to make the airplane turn.
Context Anchor
You will see this term in aircraft control, turn, attitude, and flight-instrument discussions.
Derivation
From the older sense of 'bank' meaning a sloped or tilted surface (as in the bank of a river or a banked roadway). When an aircraft tilts its wings, it is leaning into the turn the same way a banked road leans into a curve.
Why Pilots Care
Correct bank angle produces coordinated turns, prevents slips or skids, and increases load factor in steeper turns.
Analogy
Like leaning a bicycle into a curve so it turns without falling over.
Intuition Check
Bank does not mean a financial bank here. In flying, it means the airplane’s wings are tilted left or right.
Example Sentence 1
The instructor asked the student to roll into a 30-degree bank to the left and hold it through the turn.
Example Sentence 2
In a steep bank the airplane requires more back pressure to maintain altitude.