J2EE

Can anyone sum up the key differences between:

JSP, Servlets etc as run on something like Tomcat
and
EJB

As far as I can tell JSP/servlets are more aimed at dynamic web content, and EJB at java systems that aren't delivered via html.
Is this right? I can't find any pages discussing the differences and rather worryingly our lecturer on Enterprise Computing doesn't have a clue.

Just hoping to confirm I'm not barking up the wrong tree.

Thanks