What is the meaning of clustering your application in EJB?

I have come across the term "clustering your application" a few times in EJB, except, I don't have any idea of what it actually means, could somebody briefly explain what it means or point me to the right resources for further reading, many thx.
[253 byte] By [SheepSheepa] at [2007-11-27 2:44:02]
# 1
Hello,This can give you a quick overview of clustrering http://www.oracle.com/technology/oramag/oracle/03-jul/o43devejb.htmlRegards,Sebastien Degardin
sdegardina at 2007-7-12 3:10:15 > top of Java-index,Enterprise & Remote Computing,Enterprise Technologies...
# 2

Typically clustering is used to provide high availability of service even in the presence of failures (of instances in the cluster). Clustering allows your client applications to continue to work properly even if one (or some) of the server instances fail.

You may find relevant info from these links:

http://wiki.glassfish.java.net/gfwiki/Wiki.jsp?page=GlassFishV2Architecture

https://glassfish.dev.java.net/javaee5/build/GlassFish_LB_Cluster.html#failover

http://developers.sun.com/appserver/reference/techart/load-balancing.html

Mahesh.Kannana at 2007-7-12 3:10:15 > top of Java-index,Enterprise & Remote Computing,Enterprise Technologies...