Period of Oscillation

the smallest interval of time in which a system undergoing oscillation returns to the state it was in at a time arbitrarily chosen as the beginning of the oscillation. Strictly speaking, the concept of period of oscillation is applicable only when the values of a quantity recur exactly over equal time intervals—for example, in the case of harmonic oscillation. However, it is also used in a broader and less strict sense for cases of approximately recurring processes.