A specific manifestation of the Wigner distribution (also the Wigner-Ville distribution) is the
frequency vs.
time dependence of some time dependent
signal. Specifically, it is the
Fourier transform of the
autocorrelation of the time domain signal -- roughly what you'd get by lining up the Fourier transforms of various segments of the time domain signal (technically that's more of a
spectrogram, though). The Wigner distribution can be applied to any
Fourier pairs. It was first applied to the
momentum/
space conjugates of
quantum mechanics (see
Heisenberg uncertainty principle).
For more info, see the writeup Fourier transforms, Wigner distributions, and Wavelet transforms.