Shielded Cable and Balanced Signal

[Pickinator]

I'm trying to gain an education about a few concepts.

A bass head has the ability to put out a balanced or unbalanced line-level signal. What does that mean? I know what a line level signal is (un-amplified) but what is balanced vs unbalanced?

What is shielding and a shielded cable/cord?

Thanks folks. I appreciate the schooling.

[seamonkey]

Start at wikipedia, then read a textbook, and a sound reinforcement guide
Balanced audio - Wikipedia, the free encyclopedia

[B-string]

BTW line level is amplified above instrument level. Shielded cables must be used with low level signals no reduce extraneous noise (like hum, whines, crackles even AM radio). Un-balanced (two lead, signal and ground/shield) are limited as to how much length and not the best at noise rejection. This shows up stronger with high gain systems (like PA apps). Balanced are two wire with a separate shield (that one side of the shield can be lifted from "ground" if needed in high RF conditions). The shield can become an antenna in high RF fields (or also ground loops) but can't be defeated in an un-balanced cable.