The term deep web is a rather imprecise term used to refer to sites and services generally not discoverable using traditional search engines. These sites have removed themselves from the search engines, either by explicit request or by including directives to prevent indexing. The intent is that only those who have a URL to such a site would know about its existence.
Since search engine removal requests and “don’t index” directives are not enforced, sites on this “deep web” can still theoretically be discovered using non-compliant search engines and spiders.
The deep web is distinct from the dark web, an equally general and imprecise term referring to sites that cannot be directly accessed on the public internet.
The deep web, invisible web, or hidden web are parts of the World Wide Web whose contents are not indexed by standard web search-engines. This is in contrast to the "surface web", which is accessible to anyone using the Internet. Computer-scientist Michael K. Bergman is credited with coining the term in 2001 as a search-indexing term.
The content of the deep web is hidden behind HTTP forms[vague] and includes many very common uses such as web mail, online banking, private or otherwise restricted access social-media pages and profiles, some web forums that require registration for viewing content, and services that users must pay for, and which are protected by paywalls, such as video on demand and some online magazines and newspapers.