"SDK" stands for "Software Development Kit", an older name for the tools used to develop
Java apps. Sun changed the name of the kit the "Java Development Kit" some time ago. One uses the JDK to write applications using the J2SE, or "Java Standard Edition" API (
J2SE ).
J2EE, on the other hand, is the "Java Enterprise Edition" and contains a bunch of components built on top of the J2SE. These include
servlets, EJB's, email, and other business-oriented API's.
Does that make sense?