for example eclipse plugin.

All that means is your client end has some intelligence.  A thin
client just has a browser capable of displaying HTML.

It might be an Applet or a JAWS app.  It could get compact binary
data, serialised objects, etc using either HTTP or socket calls back
to the server.  It might even talk JDBC though that is usually
considered poor form.  You get a servlet to do the JDBC and pass the
raw data back.

A rich client also might help a client fill in a complex input form,
validating as you go, automatically skipping unneeded fields,
automatically looking up codes and validating as it goes. Filling in
thin client HTML forms is far clumsier than what we did in the DOS
days.

If you are looking for some student projects that might be implemented
as rich clients see http://mindprod.com/projects/projects.html