Leakage

Leakage, more explicitly called spectral leakage, is a smearing of power across a frequency spectrum that occurs when the signal being measured is not periodic in the sample interval. It occurs because discrete sampling results in the effective computation of a Fourier series of a waveform having discontinuities, which result in additional frequency components. Leakage is the most common error encountered in digital signal processing, and while its effects cannot be entirely eliminated, they may sometimes be reduced with the aid of a suitable apodization function.