In J2EE application modules are packaged as EAR, JAR and WAR based on their functionality
JAR:
EJB modules which contains enterprise java beans class files and EJB deployment descriptor are packed as JAR files with .jar extension
WAR:
Web modules which contains Servlet class files, JSP FIles, supporting files, GIF and HTML files are packaged as JAR file with .war (web archive) extension
EAR:
All above files (.jar and .war) are packaged as JAR file with .ear (enterprise archive) extension and deployed into Application Server.