Glossary - R

ranking
Referring to the position of a web page on the search results for a particular query . For example, a page that is listed third for the term "bubblegum" is said to have a ranking of 3 for that term.

recall
A measure of a search engine 's ability to return all relevant results. Search engines must find a balance between recall and precision (The measure of a search engine's ability to return only relevant results). If there are 10 pages about "blue bananas" in a search engine's database and a search for "blue bananas" returns only 8 of those pages, the recall is scored at 0.8 or 80%. It's important to note that recall has nothing to do with database size. If another search engine has only 3 pages about blue bananas and returns all 3, its recall is 100%, even though there are other relevant documents not included in its database.

reciprocal link
A link placed on site A, pointing to site B, on the condition that site B returns the favor. Also called a link swap. Contrary to popular belief, reciprocal linking does not necessarily improve a site's PageRank . In some cases it can have a negative effect on PageRank.

redirect
Users can be redirected from one page to another either by asking them to click on a link or by means of automatic redirection, most often done with the meta refresh tag. Automatic redirection has been misused to the point where most search engines now penalize sites that use it, typically by de-listing the offending site.

referrer
When a user follows a link from page A to page B, page A is called the referrer. The referrer is identified by the URL of the referring page. Referrer information can be accessed through the log file .

relevance / relevancy
The measure of the accuracy of the search results - in other words it's a measure of how close the documents listed in the search results are to what the user was looking for. The ability to return relevant results is a big thing in the search engine world - and arguably the one thing that made Google stand out of the crowd and gain much popularity in a short time.
Also see precision and recall .

re-submission
The process of submitting a web page to a search engine and then repeating the submission process - either a couple of times or regularly over a period of time. Contrary to popular belief, regular re-submission does not improve a page's ranking and is considered a form of spamdexing by most search engines.

robot
A browser -like program that automatically request web pages in order to index the page content (in the case of spiders ) or to retrieve specific information (in the case of programs like e-mail harvesters).

robots.txt / robots text file
A text file (with the ".txt" extension) that tells spiders which pages it may not index . Every time a spider (that complies with the Robots Exclusion Standard) visits a site it will first request a robots.txt file to see where in the site it is not allowed to go.

ROIReturn On Investment. In the context of SEO , the term refers to sales generated as the direct result of a search engine marketing campaign.

R/S ratio
The ratio of the number of web sites which contain a keyword or keyphrase ("R", the supply) to the number of search engine searches for that keyword or keyphrase ("S", the demand). Used as to identify attractive keywords for which there is little competition.