So you can speak SEO fluently...

Backlink
Links originating outside a web site, pointing to that web site. An external incoming link.
Black Hat SEO
The use of unaccepted SEO practices to increase page rank. Can jeopardize your rank if you are removed from search results as a penalty.
Doorway Page
Also known as a gateway or bridge page. Exists only for the purpose of driving search engine traffic to another page, made specifically to trick search engines into ranking a page high for certain keywords in search results. A Black Hat technique.
Google AdSense
A contextual advertising program. Text, images or video ads are embedded on your web site that generate revenue. Google controls the content of the ads.
Google AdWords
A form of Pay Per Click advertising. Your ad appears in a premium seciton of the search results page when your ad words are searched for.
Keywords
The most important words or phrases that capture the essence of what you want to communicate with your web site. Various online tools can be used to determine what the most popular searches are to refine the words and phrases you make prominent in on-page and off-page optimization.
Landing Page
A page constructed to provide rich content on a specific topic.
Organic Search
Listings on search engine results pages that appear because of their relevance to the search terms, as determined by the search engine's algorithm rather than advertisements.
Non-Organic Search
Search results that are ranked due to pay per click or other advertising.
Natural Search
Same as Organic Search
On-Page Optimization
HTML tuning practices involving changes to your web site, some visible, and many invisible to site viewers, to optimize the technical elements of your site for keyword searches.
Off-Page Optimization
Link building and article writing that constructs links pointed to your web site.
Page Rank
Placement of your page in rank order, compared to other results using the same search terms.
PPC
Pay Per Click: Advertising by paying a negotiated set amount whenever someone clicks on an ad.
Reciprocal Link
Trading links with another web site. Once used widely to increase page rank, but no longer effective and can actually harm your rank unless the link relates directly to the page content.
SEM
Search Engine Marketing: gaining traffic from search engines through free SEO efforts or paid advertising.
SEO
Search Engine Optimization: the process of improving the visibility of a website or a web page in search engines via free organic search results.
SERP
Search Engine Results Page
SMO
Social Media Optimization
Spider
Web crawlers and bots that electronically follow links to index web pages.