Side chain. What is it? What is it used for?

Side chain. What is it? What is it used for?
Certain items of sound engineering equipment have 'side chain' inputs. What exactly is a side chain, and what can you do with it?
Source: www.record-producer.com

Kanye West: Hip-hop artist of 2005
So much goes into the mix when choosing an artist of the year. Not only should the artist be at the top of his/her musical game, they must be highly visible in a way that impacts the world outside of...
Source: rap.about.com

How Do CDs Work?
How do CDs work? How should you look after a CD? A knowledge primer for better CD mastering...
Source: www.record-producer.com