Definition:Harmonic Wave/Frequency

Definition
Let $\phi$ be a harmonic wave expressed as:
 * $\forall x, t \in \R: \map \phi {x, t} = a \map \cos {\omega \paren {x - c t} }$

The frequency $\nu$ of $\phi$ is the number of complete wavelengths of $\phi$ to pass an arbitrary point in unit time.

Also see

 * Frequency of Harmonic Wave: this frequency is shown to be $\dfrac 1 \tau$, where $\tau$ is the period of $\phi$