MIDI CC (Control Change)
The MIDI message for turning knobs: 128 numbered controllers per channel, each holding a value from 0 to 127.
A CC message is three bytes: the status byte 0xBn (n being the channel), the controller number and the value. A handful of numbers got fixed meanings back in MIDI 1.0 in 1983 and have kept them ever since: CC1 is the mod wheel, CC7 volume, CC10 pan, CC11 expression and CC64 the sustain pedal, where anything from 64 up counts as pressed. The rest is a free-for-all, which in practice means every synth ships its own table in an appendix of the manual.
Seven bits produce audible stair-steps on a slow filter sweep. The fix was pairing CC0–31 with CC32–63 into 14-bit values, which few manufacturers bothered with. In a DAW the CC stream is what gets recorded and drawn as automation lanes. CC120–127 are reserved for channel mode commands such as All Notes Off, the panic button for stuck notes.