Variable Names and Definitions

If anyone could point me to the listing of all the possible Variable Names, and what their output is, I would greatly appreciate it. For example, by default $title (used in most themes) displays both the node Title and the Submission information.

I want the flexibility of using different Variable, but an unable to locate a definitive list at this time. I suspect that my problem is one of vocabulary. I consider $head, $frontpage, $mission, $breadcrumb, etc. to all be Variables, and that a list of all the possible Variables would have been located in the "Drupal 6 Theme guide".

But I'm not seeing what I'm expecting to see, which is additional Variables that can also be used in the templates to break out other information, like *only* the title and no Submission information.

I'm guessing some other terminology is used to identify this field? Any guidance or clarification is greatly appreciated. Thank you!