Search Engine Terms Defined Resources

Links that start on another site and point to yours. An example of backlinks optimization would be to incorporate specifics of anchor text in the links if possible.
Boolean operators
Used for a combination of terms allowing inclusion or exclusion of certain words. Some Boolean operators include AND, OR, NOT, ADJ, etc.
Internationally deceiving users or presenting different content to search engines than you display to users.
descriptive text accompanied by a title and URL in the search results page. Some search engines take this description from the meta description while most generate their own from the page content.
A word used in a query.
Keyword Density
Keyword density measures the relationship of keywords to other text. A high percentage of keywords in relationship to other text suggests that this keyword is important. Here's an example of how it's measured. Let's assume the keyword phrase is "sheet metal fabrication." Sheet metal fabrication is our primary business. In the above example, "sheet metal fabrication" makes up about half the words in that sentence. If it were the only sentence on a page, a search engine could conclude that "sheet metal fabrication" is important.
Keyword Frequency
Keyword frequency is a measure of the number of times keywords occur within a page's text. It's tied to the concept of keyword density. Search engines want to see more than one repetition of a keyword in your text to make sure it's not an isolated case and is actually important to your site. This factor is easy to consider. You will almost always naturally use your most important keywords more than once on a page. If this is not the case, write a few coherent and user-friendly sentences that mention your important terms.
Keyword Prominence
Search engines prefer to see the most important keywords appear prominently on a page. "Prominent" means that the keywords should be part of one of the highlighting content tags or be placed on in a notable place on your pages - such as the top of the page.
"stop words"
Particles like "and", "the", "a", "an", etc. usually used for flow of language structure. "Stop words" are usually discarded by search engine spiders.
"Google bombing"
Multiple sites linking to the same site, with the same anchor text in order to get high ranking for the keyword in the anchor text.
"Google sandbox"
Implications that new sites, no matter how well optimized, don't rank high on Google searches.
Meta tags
An HTML tag placed in the head section of a web page that provides additional information that is not displayed on the page itself. The initial idea was that webmasters should use these tags to help search engines index the page correctly by providing an accurate description of the page content and a list of keywords associated with the page.
Query or query terms
Words or keywords or phrases entered into a search box or form to perform a search query.
Search Engine Optimization (SEO)
Term used in the search engine industry as a collective name for activities that are directly or indirectly aimed at improving a Web page's search engine ranking.
Search Engine Results Page(s) (SERPS)
The term refers to the page of search results a search engine displays in response to a query.

See also: Search Engine Dictionary provides a very good glossary and extensive of search engine terms.