Or more generally, it’s the correlation of your signal with a set of sine waves of different frequencies. It doesn’t have to be a sine wave. You could correlat

Or more generally, it’s the correlation of your signal with a set of sine waves of different frequencies. It doesn’t have to be a sine wave. You could correlate your signal to a fart sound (or a set of them). It’s a valid transform but it would not be invertible—given a vector of scalar values showing how much your signal resembled each type of fart, you could not reconstruct the original signal. However you can do that with the FT. It’s invertible and you can recover the signal from the spectrum. So in some sense it doesn’t lose information. Energy in the signal is equal to energy in the Fourier spectrum.