Definition
A property of a spinning rotor (such as a propeller or gyroscope) in which a force applied to the rotor produces a reaction not at the point where the force was applied, but at a point 90 degrees ahead in the direction of rotation.
Plain English
When you push on something that is spinning fast, it does not react where you pushed. The reaction shows up a quarter-turn later, in the direction the spin is going.
Context Anchor
Seen when studying propeller effects, aircraft control during nose-up or nose-down changes, and the behavior of gyro-based flight instruments.
Derivation
Gyroscopic comes from the Greek gyros (circle, ring) and skopein (to look at) -- literally a device for observing rotation. Precession comes from the Latin praecedere, meaning to go before or move forward. Together the term describes how the effect of a force on a spinning object 'goes ahead' of where it was applied.
Why Pilots Care
It produces unwanted yaw when the nose is raised or lowered, requiring timely rudder correction to keep the airplane coordinated.
Analogy
Think of a fast-spinning bicycle wheel held in your hands. If you try to tilt it one way, it may feel like it wants to move in a different direction. That strange-feeling response is the same basic idea.
Grounding Statement
A spinning object in an airplane can react to a push as though the push happened about one quarter of a turn later.
Intuition Check
Gyroscopic precession does not mean the spinning object simply moves in the same direction you push it. The key idea is that the main reaction appears about 90 degrees later in the direction of spin.
Example Sentence 1
As the tail came up on the takeoff roll, gyroscopic precession yawed the nose left, and the pilot countered with right rudder.
Example Sentence 2
Lowering the nose after a stall produces a right yaw in most American engines because of gyroscopic precession.