Definitions for "Perturbation"
A disturbance in the regular elliptic or other motion of a heavenly body, produced by some force additional to that which causes its regular motion; as, the perturbations of the planets are caused by their attraction on each other.
A non-random disturbance.
disturbance in the normal movement of an orbiting body arising from an external force, usually gravitational.
A slight nudge.
A small nudge or displacement of a dynamical system from its current state, either by an external force or random variation.
Any confusion, disorder or mistake that signals a " problem". [D03667] DSMC
Keywords:  agitation, esp, mind, act, disorder
The act of perturbing, or the state of being perturbed; esp., agitation of mind.
the act of causing disorder
A forced change to a system. This can result in a sudden shift to a new state, an immediate return to the old state or a long transient resulting in one or the other.
(physics) a secondary influence on a system that causes it to deviate slightly
Any effect that causes a small change in a physical system and/or changes the value of some given function.