Newbie question - overlays I guess

Newbie question - overlays I guess

Hello

I've been playing with jQuery for about a month now and have gotten various addordian panels to work as well as the obligatory tool tips and modal boxes. For my next trick I wanted to see how to get an expanding panel setup link the one at the bottom of this page. Click the button that saus "I need to +" and the organge panel/window that expands. Is there a generic term for these and can anyone lead me to a resource that talks about these in their simplest form?

http://www.imulus.com/portfolio

I say simplest because I am not sure I need or want a plug-in. Actually, I haven't really internalized how a plugin differs from some of the base functionality of the framework. Would jQuery UI be considered a plugin. The reason I'm asking is that I'd rather try to figure out what the elements and not have a plugin wrapper mask all the details. Unless it's really needed to accomplish this type of thing.

Cheers
Rich