1) How Search Engines Work
The term "search engine" is often used generically to describe both crawler-based search engines and human-powered directories. These two types of search engines gather their listings in radically different ways.

2) Link Popularity
Link Popularity is basically a measure of the number and quality of inbound links to your website. It refers to the total number of links or "votes" that a search engine has found for your website. It is one of the best ways to measure a website's online awareness and overall visibility. At the simplest level, the more sites that link to your site, the more important your site will be regarded.

That's the straightforward explanation - it's actually a little more complicated than that. Search engines will also look at the quality and relevance of the links... in addition to other factors. (In some instances, they'll even look at the words being used to provide the link.)

Some Search engines use this assessment when determining rank and positioning. One very important search engine that has placed a great deal of emphasis upon link popularity is Google. This excellent search engine uses what it calls PageRank(tm) as an indicator of a page's value. Without a good Google PageRank, you are unlikely to appear high in Google search results. And, since Google is such an important search engine, it's essential that
you strive for a site with good link popularity if you're looking to attract visitors. Some of the other leading search engines which use link popularity criteria are AltaVista, Excite and HotBot.

3) What is SPAM?
SPAM is the use of any tactic that attempts to mislead a search engine about the
relevance of your site to the search phrases, typical examples of this are the use
of doorway pages with redirect scripts, white text on white background etc.