A Search Engine is an information retrieval system designed to help find information stored on a computer system. Search engines help to minimize the time required to find information and the amount of information which must be consulted, akin to other techniques for managing information overload.

The most public, visible form of a Search Engine is a Web Search Engine which searches for information on the World Wide Web. Examples of popular search engines would be Google, Yahoo, Microsoft’s Live, AOLand Ask.

Search engines provide an interface to a group of items that enables users to specify criteria about an item of interest and have the engine find the matching items. The criteria are referred to as a search query. In the case of text search engines, the search query is typically expressed as a set of words that identify the desired concept that one or more documents may contain.

To provide a set of matching items quickly, a Search Engine will typically collect metadata about the group of items under consideration beforehand through a process referred to as indexing. The index typically requires a smaller amount of computer storage, and provides a basis for the Search Engine to calculate item relevance. The Search Engine may store a copy of each item in a cache so that users can see the state of the item at the time it was indexed or for archive purposes or to make repetitive processes work more efficiently and quickly.