A portlet is a Java-based Web component that processes requests and generates dynamic content.
Portlets are componentized user-facing applications that create some kind of markup.
Java Portlet Specification v1.0 - 7~11
Introducing the Portlet Specification, Part 1
What's new in the Java Portlet Specification V2.0 (JSR 286)?
http://www.unicon.net/node/730
http://blog.naver.com/echan76?Redirect=Log&logNo=140022998455
http://portals.apache.org/pluto/
http://portals.apache.org/jetspeed-2/