When looking at job openings on-line, I noticed that some openings required knowledge of \"core Java\". What is core java and how is different from java?
It's not an official term. I guess it means knowledge of the Java language itself and the most important parts of the standard API (java.lang, java.io, java.utils packages, basically), as opposed to the multitude of specialzed APIs and frameworks (J2EE, JPA, JNDI, JSTL, ...) that are often required for Java jobs.