Sample rate determines the frequency range a digital recording can capture. The standard for music is 44.1 kHz (CD quality) or 48 kHz (video/broadcast). Higher rates like 96 kHz or 192 kHz are used in professional recording for extra headroom during processing.
According to the Nyquist theorem, a sample rate captures frequencies up to half its value. Since human hearing tops out around 20 kHz, 44.1 kHz covers the full audible range.
When buying or selling stems, sample rate compatibility matters. Mixing stems recorded at different sample rates can cause pitch and timing issues.