Nyquist frequency

A property of a chosen sampling rate: half of $f_s$ , the highest frequency that rate can represent without aliasing.

The Nyquist frequency of a sampling rate $f_s$ is $f_s/2$ -- the highest frequency that rate can represent without aliasing. It is a property of the chosen rate, not of any particular signal being sampled with it. The Nyquist-Shannon theorem's guarantee, $f_s>2B$ , can be restated as $f_s/2>B$ : the chosen rate's Nyquist frequency must exceed the signal's bandwidth. Not to be confused with the Nyquist rate, a property of the signal instead -- the two coincide only at the boundary case $f_s=2B$ .

Examples

A recording made at $f_s=48$ kHz has Nyquist frequency $48/2=24$ kHz, regardless of what signal was actually recorded.