Wikipedia Answer:
A word clock or wordclock (sometimes sample clock, which can have a broader meaning) is a clock signal (not the actual device) used to synchronise other devices, such as digital audio tape machines and compact disc players, which interconnect via digital audio. S/PDIF, AES/EBU, ADAT, TDIF and other formats use a word clock. Various audio over Ethernet protocols use broadcast packets for the word clock. The device which maintains the word clock on a network is the master clock.
Word clock should not be confused with timecode; word clock is used entirely to keep a perfectly-timed and constant bitrate to avoid data errors. The word clock generator, usually built-in to Analog to Digital converters, creates digital pulses which contain no other data, and is considered essential to avoid frequency drift between the internal oscillators of each device. Timecode is actual data (technically metadata) about the media content being transmitted, and is optional, being sent in a higher layer.
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Novice answer:
Basically you can connect all of you digital gear together via the BNC cable usually 75 Ohm for audio.
PC Audio cards can have them, AD/DA Converters can have them, Line 6 POD Pro's have them.
From my limited understanding, you can set one device as a Master Clock be it your Audio Card or AD/DA converter, then feed the BNC cable in a loop through all your digital gear which puts everything on the same clock cycle.
In the end it helps prevent clock errors which can cause little clicks and pops on your recording.
You can usually accomplish the same with optical connections without the BNC cable. With the BNC most devices will be set to External and I hear that it is generally the most effective way to Sync your Clock Signals.
Anyone else feel free to chime in........
