center of gravity - The point on an airplane where the entire weight of the airplane is considered to be concentrated. The location of the center of gravity is an important factor in a stable airplane.

equilibrium - The ability of an airplane to maintain balanced flight during which all the forces and moments acting on it equal zero. That means lift = weight, and thrust = drag and there are no rotating moments acting on it.

longitudinal - The ability of an airplane to pitch itself back into a state static stability of equilibrium after being disturbed along its longitudinal axis.

neutral static - The tendency of an airplane to hold the new angle of stability attack it encounters after having its flight disturbed.

stability - The tendency, or lack of it, of an airplane to fly a prescribed flight condition or in steady flight.

static stability - The tendency of an airplane after being disturbed to generate its own restoring forces that bring it back to its initial state of equilibrium.

statically unstable - The tendency of an airplane after being disturbed to continue its new motion without being able to return on its previous state of equilibrium.

trimmed flight - The attitude held by an airplane at which it will continue in level flight without the pilot having to exert additional control.

turbulence - a disturbance in the airflow around an airplane that causes a disruption in its equilibrium.