A Fourier transform (FT) is a mathematical method used to transform signals from the time domain to the frequency
domain. It is thus used to determine the frequency spectrum of a time-related signal. The Fourier transform of a pure sinusoidal signal from the time domain to the frequency domain results in a single spectral line. All other non-sinusoidal signals such as square wave signals, modulated signals, pulses, etc., consist of a fundamental wave and several harmonics that differ in amplitude
.Fast Fourier Transform (FFT). The inverse of the Fourier transform, i.e. the transformation of a frequency-related function into a time-related one, is called inverse Fourier transform. The name of the transformation goes back to the French mathematician Baron Jean Baptiste Joseph Fourier, who lived from 1768 to 1830.