Word of the Week – Google PageRank
Google PageRank is an algorithm used by Google to determine the weight of a set of linked (or hyperlinked) web pages. It is one of the (assumed to be) primary pieces of the larger Google Search algorithm which determines order of appearance in a keyword search.
A larger number of quality links from high PageRank sites will increase your PageRank.
Of course, that is the condensed version, for a complete and technical explanation of PageRank, I would recommend the PageRank article on Wikipedia.