This is an old revision of the document!
PCB is short for “Printed Circuit Board”. One way to think of them is as a stencil or blueprint for a circuit or device. When a PCB is made, the task of putting together a circuit is much easier, since all the connections are premade– it's just a matter of mounting individual parts.
One issue to note for those new to soldering(at least, one issue that I had): It's possible for the etching on a PCB to come up if heat from the soldering iron is misapplied or applied too much. While this is a real hassle, it should be possible to solve by bridging either with insulated wire(soldering one end to each side of the formerly-closed circuit path) or by some other means.
One way to avoid this is to get a good desoldering tool. RadioShack has a couple, one of which is a simple trigger-operated vacuum, and the other is a combination soldering-iron-and-vacuum with a squeezebulb for intake. This seemed a bit strangely designed to me, plus it was 45 watts which would probably toast something.
In short, it's best to get practice soldering before one messes up a MIDIBox CoreModule!
PCBs for MIDIBox modules can be found at SmashTV's website http://mbhp.avishowtech.com as well as at a German site I can't remember the URL for.