Plain English Meaning
Pitch is the up-and-down movement of the airplane's nose. Pull back and the nose rises; push forward and the nose drops.
Full Definition
Rotation of an airplane about its lateral axis, raising or lowering the nose relative to the horizon. Pitch is controlled primarily by the elevator and is one of the three axes of flight, along with roll and yaw.
Context Anchor
You see this term in basic flight-control discussions, especially during climbs, descents, takeoffs, landings, and any time the pilot raises or lowers the nose.