Sinusoid ($A\cos (\omega t+\varphi )$)

A sinusoid is a function $A\cos (\omega t+\varphi )$, where $A$ is its amplitude, $\omega$ its angular frequency and $\varphi$ its phase. For $\omega \ne 0$ its period is $2\pi /|\omega |$. A uniformly randomized phase can produce a strictly stationary process even though individual paths look periodic.