Radio button - A round selection (check box) field in software programs and Web forms that when checked, looks like a knob from an old radio.

RAM (Random Access Memory) - Temporary memory that your computer uses to store information. Text copied to the "clipboard" is stored in RAM until it is replaced by new information or the computer is turned off.

Rankings - The order in which individual Web pages are returned in the SERPS for a given search query. Search engines rank the Web pages based upon relevancy to your search terms according to their proprietary algorithm.

Reach - The portion, usually given as a percentage, of a target audience (e.g., 18- to 34-year-old males, or small businesses) that has opened a particular page or site.

Real Audio™ - A browser plug-in used to listen to live or on-demand music in real-time across the Internet at 14.4K baud or higher.

Reciprocal Links - Links to another Web site placed on your site in exchange for links back to your site from theirs. This is a proven way to build link popularity which is instrumental in getting high search engine rankings.

Recurring Payments - A type of transaction which allows the Merchant to process multiple authorizations for the same Buyer. The two kinds of recurring payments include multiple payments for a fixed amount and repeated billings.

Referrer - The URL of the Web page from which a unique visitor came.

Registration - The process of informing a search engine or directory that a new Web page or Web site should be indexed.

Relevancy Algorithm - The method a search engine or directory uses to match the keywords in a query with the content of each Web page, so that the Web pages found can be ordered suitably in the query results. Each search engine or directory is likely to use a different algorithm, and to change or improve its algorithm from time to time.

Relevant Content - Content or copy that is relevant to the users search request. If you want to rank high for a particular keyword, you need to have relevant content for that keyword on the actually Web page targeting that keyword.

Remote Login - Operating on a remote computer, using a protocol over a computer network, as though locally attached.

Retention - The measurement of unique users who return to the same site or page over a given time. PC Data Online, for example, measures it as "the percentage of a site's traffic during the previous month that also came back during the current month."

Robot ("bots" and personal agents) - Any browser program which follows hypertext links and accesses Web pages but is not directly under human control. Examples are the search engine spiders, the "harvesting" programs which extract e-mail addresses and other data from Web pages and various intelligent Web searching programs.

Robots.txt - A text file stored in the top level directory of a Web site to deny access by robots to certain pages or sub-directories of the site. Only robots which comply with the Robots Exclusion Standard will read and obey the commands in this file.

ROI - Return on Investment.

Routing - The process used on the Internet to deliver data packets to their intended destination. A router processes the data packet and reads the destination address included in the IP header then determines the next (router) stop that will take the packet closer to its destination. The process is repeated until the packet arrives at its final target.