In order for a band-limited (i.e., one with a zero power spectrum for frequencies 
) baseband (
) signal to be reconstructed fully, it must be sampled
at a rate 
.
A signal sampled at 
is said to be Nyquist sampled, and 
is called the Nyquist
frequency. No information is lost if a signal is sampled at the Nyquist
frequency, and no additional information is gained by sampling faster than this
rate.
Sampling Theorem
See also
Aliasing, Nyquist Frequency, Nyquist Sampling, OversamplingExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Sampling Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/SamplingTheorem.html