Plain English Meaning
How high or low the nose of the airplane is pointing compared to the horizon.
Full Definition
The angle between the airplane's longitudinal axis (nose-to-tail line) and the horizon, as seen from the side. A nose-up pitch attitude means the nose is raised above the horizon; a nose-down pitch attitude means the nose is below it.
Context Anchor
You see pitch attitude when looking outside at the airplane’s nose against the horizon, and you use it when controlling the airplane during climbs, descents, slow flight, and stall recovery.
Derivation
Pitch' in aviation comes from the older nautical sense of a ship rocking nose-up and nose-down in the waves. 'Attitude' here comes from the Latin 'aptitudo,' meaning posture or — the way something is held. Together: the nose-up or nose-down posture of the airplane.