Here's how I usually explain it:
Hypersite - like a web site with no navigation. You can save multiple web pages to it, and they all have the same start URL (eg. web1.yourcompanyname.com). It can host both Generic and PURL pages.
Generic landing page - its like a standard web page. And you can name the url (web1.yourcompanyname.com/myawesomelandingpage)
PURL page - a web page that can be personalized for a specific visitor using Eloqua's dynamic content features