difference between webdynpro application and webdynpro component

Hello experts,

what is the difference between webdynpro application and webdynpro component ?

In the Launchpad (lpd_cust), I see webdynpro applications (e.g hress_a_benefits) specified, but when I

try to open it from se80, it's not showing.

How do I access webdynpro application from backend ?

Thanks

Raghu