Aliasing
Distortion caused when a sampled signal cannot uniquely represent frequency content above the Nyquist limit, folding higher frequencies into lower apparent frequencies.
Aliasing occurs when the sampling rate is insufficient to distinguish frequency components, causing different analog frequencies to appear as the same or incorrect lower-frequency digital components.
Sampling Context
Aliasing occurs when a continuous-time signal contains frequency components that cannot be represented uniquely at the selected sampling rate. Those components fold into lower frequencies after sampling and cannot be removed reliably from the sampled data.
Measurement Boundary
Aliasing is not the same as spectral leakage. Leakage is caused by finite-time windowing; aliasing is caused by insufficient sampling bandwidth.