Phase shift
= Phase shift
{title2=$\Delta\phi$}
A <phase shift> is a change in an oscillation's <wave phase>, specified modulo $2\pi$. It can arise from propagation, reflection or an imposed response. With the time convention $e^{-i\omega t}$, a delay $\tau$ multiplies the <complex amplitude> by $e^{i\omega\tau}$. A sign reversal is a $\pi$ <phase shift>.