Every digital device has an internal clock that determines when each sample should be captured (recorded) or reconstructed (replayed). This is the “word clock” — a digital clock that governs the sample rate of the device. Some devices offer a word clock output so you can use the word clock in that device to synchronize the sample rate of other digital devices. Some devices offer a word clock input that allows them to use the word clock coming from another device (such as a master clock) instead of their own internal word clocks. Word clock is typically carried over BNC connections, though many audio devices can also synchronize their clocks via AES/EBU, S/PDIF, or optical ports. It is essential to synchronize the clocks in devices that are connected digitally to ensure accurate signal transmission.
“Clock sync” refers to a signal that is used to synchronize the tempo of the musical performance generated by musical instruments and devices such as drum machines, workstation keyboards, sequencers, and computer-based DAWs and other software. Think of it as a “metronome” that keeps the tempo of these devices locked together. For clock sync, you need two or more devices that speak the same synchronization language, such as MIDI clock. One device serves as the “master” and others slave their tempo to that master.