Sample rate is how many times per second an analog-to-digital converter measures the incoming signal, expressed in kHz. The Nyquist theorem sets the ceiling: a 48 kHz rate can represent frequencies up to 24 kHz, just past the limit of human hearing. Video settled on 48 kHz because it divides cleanly against common frame rates and yields a whole number of samples per frame, which keeps audio and video aligned. 44.1 kHz survives from the CD era and still appears in music. Production formats use 96 or 192 kHz for extra headroom during pitch-shifting and time-stretching, then downsample to 48 kHz for delivery.
