Class C Blocks: refers to part of your site's IP address.
255.255.XXX.YYY - X 's identifies the class C Subnet
CPC: The Cost Per Click indicates how much you will pay for each click in a Paid Search Engine Marketing campaign.
CPO: The Cost Per Order is the average amount you will end up investing to get one paying customer through a Paid Search Engine Marketing campaign.
Directory: A database/listing of web sites usually organized in categories within categories.
Inbound Link: Tell search engines that your page is important. A Link to your page from an important site that uses your keywords in the anchor text of the link will likely produce a more positive ranking effect than all of your other ranking efforts combined.
Keyword Density: Keywords as a percentage of indexable text words. Generally, keyword density should be high enough that a keyword is recognized as a main topic of a page and not an incidental, unimportant word. At the same time, keyword density should not be too high, as some search engines may penalize a page for keyword stuffing. Other Bad SEO practices that might cause you to be penalized by Search Engines...
Link Farm: a network of sites that all host an identical links page containing links to all the network partners.
Meta tags: Meta tags are invisible data hidden in the HTML source code of a web site. The myth that these tags are vital to search engine rankings still persists today.
PageRank: Google PageRank is a proprietary system that measures the link popularity of a web site. The values are between 0 (no external sites are linked to the site) and 10 (the site has millions of in-bound links).
PPC: Pay Per Click means Paid Search Engine Marketing: Directly bidding on search terms with search engines such as Google and Yahoo! Once a visitor clicks on an ad linked to your site, you get charged for the click.
Robot: see Spider.
SEM: Search Engine Marketing. Everything that can be done to utilize the technology of search engines with the goal of promoting a web site and increasing its traffic, its "stickiness," and, in the case of sites that promote a business (or are a business), increase profits.
SEO: Search Engine Optimization. Subset of SEM. Involves modifying or enhancing a web site directly according to the most effective search terms to achieve a higher organic (natural) ranking.
Spider: The automated programs sent out by search engines to review and index websites.
Spider Food: Keywords embedded (usually invisibly) into a web page to attract search engines (spiders). The intended result of including spider food in one's web page is to insure that the page appears high on the list of matching entries to a search engine query.
SRT: Search Results Titles.
SRD: Search Results Descriptions.