Oscillation

Oscillation – a regular periodic variation in value about a mean.
Oscillation – a regular change in strength or direction in a wave or electric current.

The condition of a simple oscillatory system, processing one degree of freedom and subjected to a dissipative forse, maybe represented by the well-known linear differentional equation :
x + ax + w^2 * x = 0

Sources:

English dictionary: WolframAlpha. Computational intelligence https://www.wolframalpha.com/

Cambridge Dictionary https://dictionary.cambridge.org/

Van der Pol. On „relaxation-oscillations“ (англ.) // The London, Edinburgh, and Dublin Philosophical magazine and Journal of Science : журнал. — 1926.