A socket is a slot on an item acquired in Outlands into which gems can be inserted. These gems, created with the Jewelcrafting profession or acquired through quest rewards, can be used to provide bonuses similar to those gained from jewelcrafting or from Blacksmithing..
|This page needs more information! If you'd like to contribute, please edit this page (free ZAM account required)!|
|The Burning Crusade
For more info on this subject visit this blizzard page. 
Hope it helps