They're all different forms of default connectivity. For example, I have one of my patchbays (I use 4 altogether) all normalled. That means that whatever is plugged into 1A on the back, is automatically routed to 1B. So I have all 8 different preamps outs going to 1A through 8A in the back of the patch bay; then 1B through 8B in the back of the patch bay go straight to channels 1-8 of my firewire interface. All without any patch cables on the front.
So why have a patch bay? Why not just go from preamp to interface? Cause now I can interrupt any of the 8 signal paths via the front of the patch bay.
Y'know this looks easier in my racks than it does in print. I'd say Google the terms to see some nifty diagrams of the possible signal paths.
In the meantime--buy this guys patchbay. All 4 of mine cost more than this--and they're not as nice as the one he's selling.
I get the +4/-10dB thing...sort of. I do need to learn patch bays though, as I know I'll need one eventually and have only given them a passing glance in the past.
That's why there's Google and YouTube, so one can read up on something and then watch video's on it!