The most common way of generating a power spectrum is by using a Fourier transform and taking the magnitude of the complex coefficients. Other techniques such as the maximum entropy method can also be used to calculate the power spectrum.
In acoustics, the spectral centroid of a sound is the midpoint of its spectral energy distribution, i.e. the frequency that divides the distribution into two parts of equal energy.
Information about the spectrum during time is called the spectrogram.