Plain English Meaning
How far the wings are tipped to one side compared to the horizon. If the wings are level with the horizon, bank attitude is zero. If one wing is lower than the other, the airplane is in a bank.
Full Definition
The angle of the airplane's lateral axis relative to the natural horizon, measured as the degree to which the wings are tilted left or right from level flight.
Context Anchor
Used in attitude flying when you judge the airplane’s position by looking outside at the horizon or inside at the attitude indicator.