In short PageRank is a “vote”, by all the other pages on the Web, about how important a page is. A link to a page counts as a vote of support. If there’s no link there’s no support (but it’s an abstention from voting rather than a vote against the page).
Shorthand for PageRank: the actual, real, page rank for each page as calculated by Google. As we’ll see later this can range from 0.15 to billions.
If page A links out to page B, then page B is said to have a “backlink” from page A.