Definition of "oscillator"
(cellular automata) A pattern that returns to its original state, in the same orientation and position, after a finite number of generations.
Quotations
He has turned up a number of new oscillators of periods 2,3,4,5,6, & 8.
1989 October 26, Richard Schroeppel, “Some recent Life results”, in comp.theory.cell-automata (Usenet)