Plain English Meaning
How the aircraft is sitting in the air — whether the nose is pointing up, down, or level, and whether the wings are level or tilted to one side.
Full Definition
The position of an aircraft as determined by the relationship of its longitudinal and lateral axes to the natural horizon. Attitude describes how the aircraft is oriented in space — nose up or down (pitch) and wings level or banked (roll) — relative to the horizon.
Context Anchor
You will see this term in flight training, instrument flying, and any discussion of controlling the airplane by reference to the horizon or flight instruments.