Basic Question

Think of your master bus as a funnel. Everything you hear...every track will eventually funnel through your master bus to your speakers.

The above are good answers.

Wikipedia give the following:

An electrical bus (sometimes spelled buss) is a physical electrical interface where many devices share the same electric connection. This allows signals to be transferred between devices (allowing information or power to be shared). A bus often takes the form of an array of wires that terminate at a connector which allows a device to be plugged into the bus.

I think this is another good explanation because what we have in sonar simulates electrical hardware (a mixing board) that does the same thing.

Bouncing - I'm having difficulty finding a good definition for that one. It probably originated back when you would record your audio on something like a 24 track, 2 inch tape reel, do your mix, and then take that mix and combine it by recording - or bouncing - it to .25 inch, 2 track tape.

Like Legion said, you can do the same thing in Digital Audio Workstations. One scenario would be after you are finished mixing and you bounce the result to a single wave file. Or, you might have a soft synth that requires a heavy processor load, so you bounce the audio from that soft synth to an audio file, thus letting you disable the soft synth and free up processor cycles.

HTH