Teoma was developed at Rutger's University. Its original concept was to reward sites with “subject-specific” popularity. This is similar to the Google popularity calculator. Whereas Google gives your page points if other pages with a high PageRank link to you, Teoma gives extra credit when sites that share a similar subject matter links to you. The idea is that sites that are respected in a certain field or about subject matter will be referred to by other websites with the same sort of concept. (Like citing a source in an academic document. If many documents cite the same source, it increases the credibility of that source.)
Teoma maintains both a paid and free listings database. If you are listed on other major search engines, you will almost certainly be found by Teoma's spider. Paid listings and free listings are kept separate, and appear with a fair balance in the search results page.