Difference b/w .ear, .war & .jar ?

Can someone please tell me the exact difference b/w .ear, .jar & .war ?
& under what circumstances should a application have these files ?

One of my application has a .ear file & an other application doesnt have. Both applications use framework which is based on MVC architecture.

So can someone tell me when do we deploy .ear file ?

I always think of it in these tearms.

ear = Enterprise Application that you place in an application server
war = Web Application that you place in a web container
jar = Java Application that can be placed anywhere and can run just from a command line

Mark

JAR is used in Java Beans as a Componet Technology(COM) , applets and other application having main class that is Desktop applications.
WAR is for servlets
EAR for J2EE Server Side Component Technology(DCOM)

Any Doubt?