This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
It's a concept that indicates your application/servlet will behave appropriately if two threads are executing i.e accesing variables and/or methods at the same time. I am assuming you understand what threads are.
Bosun (SCJP, SCWCD)
So much trouble in the world -- Bob Marley