Sampling Theorem

In order for a band-limited (i.e., one with a zero Power Spectrum for frequencies $f>B$) baseband ($f>0$) signal to be reconstructed fully, it must be sampled at a rate $f\geq 2B$. A signal sampled at $f=2B$ is said to be Nyquist Sampled, and $f=2B$ 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.

See also Aliasing, Nyquist Frequency, Nyquist Sampling, Oversampling