what is glassfish application server?

Experience Sun GlassFish Enterprise Server (previously named Sun Java System Application Server)—an easy, fast, and industry-leading application server based on Java Platform, Enterprise Edition (Java EE) technology for developing and delivering web applications and web services.

Sun GlassFish Enterprise Server is Sun's commercially supported distribution of the open-source GlassFish application server from the GlassFish Community and is free for development, deployment, and redistribution.

Sun GlassFish Enterprise Server is included in the Java EE SDK—the first robust, commercial Java EE 6-compatible implementation that lets you easily develop and deploy you applications.