Variables are fields calculated from other fields, much like a cell formula in a spreadsheet. These could be used in recipe rules.
Variables, once saved, are computed for all pages on the site.
Variable could output different types such as:
* a number such as a new traffic estimation for a site (perhaps using internal CTR data for certain topics)
* a selection from a list or multiple selections, such as which question words are found in the topic keywords
* a keyword