Yelp consists of a comprehensive online index of business profiles. Businesses are searchable by location, similar to Yellow Pages. The website is operational in seven different countries, including the United States and Canada. Business account holders are allowed to create, share, and edit business profiles. They may post information such as the business location, contact information, pictures, and service information. The website further allows individuals to write, post reviews about businesses, and rate them on a five-point scale. Messaging and talk features are further made available for general members of the website, serving to guide thoughts and opinions.
In some contexts, the term SEM is used exclusively to mean pay per click advertising, particularly in the commercial advertising and marketing communities which have a vested interest in this narrow definition. Such usage excludes the wider search marketing community that is engaged in other forms of SEM such as search engine optimization and search retargeting.
Webmasters and content providers began optimizing websites for search engines in the mid-1990s, as the first search engines were cataloging the early Web. Initially, all webmasters only needed to submit the address of a page, or URL, to the various engines which would send a "spider" to "crawl" that page, extract links to other pages from it, and return information found on the page to be indexed. The process involves a search engine spider downloading a page and storing it on the search engine's own server. A second program, known as an indexer, extracts information about the page, such as the words it contains, where they are located, and any weight for specific words, as well as all links the page contains. All of this information is then placed into a scheduler for crawling at a later date.