J2SE (Java 2 Standard Edition) is the core Java platform containing the base language, fundamental APIs, and runtime environment. J2EE (Java 2 Enterprise Edition) builds upon J2SE, adding specifications for enterprise features like web services, EJB, servlets, and database connectivity. They are not entirely different technologies - J2EE depends on J2SE - and J2SE can be used in web applications, but lacks enterprise-specific features.