A parameter page is a single page containing all parameters that are passed into a rule. It is not the same as a clipboard page and does not exist on the clipboard, but offers much of the same functionality. Parameter pages are mostly handled behind the scenes for you based on your preferences on the relevant "Parameters" tabs, and whether you check the "Pass current parameter page" checkbox when calling an Activity from another Activity.
If you set a parameter to type "Page Name" it can be used as the name of a page, thus allowing you to pass an entire clipboard page as a parameter.
A Prompt Page is another way to pass a page into an Activity. If a page is set to 'Prompt' mode, then another textbox appears below the "Call" step where you can specify the name of the page to be passed to the called activity. Prompt Pages were available before "Page Name" Parameters.
Since "Page Name" parameters offer the same functionality, I believe prompt/indirect pages are considered deprecated. If I find an authoritative source that says so, I'll update this post.