Glassfish Tomcat

What is Glassfish and Tomcat for? I have searched them and it says GlassFish is an open-source application server开发者_如何学C project started by Sun Microsystems for the Java EE platform but I don't really understand. Can anyone explain to me?

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Both are server environments for running J2EE (Java Enterprise) applications. Glassfish is a full blown server implementation while Tomcat is a container implementation:

http://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition

http://wiki.glassfish.java.net/Wiki.jsp?page=FaqGlassFishTomcat