Search engines are programmes for retrieving documents in the internet that have been stored and published in a computer or computer network such as the World Wide Web (WWW).

Internet search engines have their technical origin in information retrieval systems. They produce a keyword index for the document basis in order to answer search requests about keywords with a hitlist arranged in the order of relevance. Having been given a search term the search engine furnishes a list of references to possibly relevant documents, usually presented with a title and a short extract from the documents in question. Various search procedures may be applied here.

The principal features, or ranges of tasks, of a search engine are:
The compilation and maintenance of an index (data structure with information about documents); processing of search requests and search data; Rich Media Search (finding and ordering of results); drawing up the results in the manner that makes most sense. As a rule the acquisition of data is done automatically, in the WWW by means of Webcrawler or Avatar on a single computer (PC, laptop, pad).