This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Tiles basically is a framework that implements composite pattern.
For example if you have a web application where the pages have similar structure like the header, menu,footer, content, you can use tiles to reduce the effort creating these pages.
As a framework you can integrate with other frameworks like Spring or Struts.