Boolean search: A search allowing the inclusion or exclusion of documents containing certain words through the use of operators such as AND, NOT and OR.

Concept search: A search for documents related conceptually to a word, rather than specifically containing the word itself.

Full-text index: An index containing every word of every document cataloged, including stop words (defined below).

Fuzzy search: A search that will find matches even when words are only partially spelled or misspelled.

Index: The searchable catalog of documents created by search engine software. Also called "catalog." Index is often used as a synonym for search engine. Index is commonly pluralized as "indices." However, Search Engine Watch instead uses the alternative plural form "indexes."

Keyword search: A search for documents containing one or more words that are specified by a user.

Phrase search: A search for documents containing a exact sentence or phrase specified by a user.

Precision: The degree in which a search engine lists documents matching a query. The more matching documents that are listed, the higher the precision. For example, if a search engine lists 80 documents found to match a query but only 20 of them contain the search words, then the precision would be 25%.

Proximity search: A search where users to specify that documents returned should have the words near each other.

Query-By-Example: A search where a user instructs an engine to find more documents that are similar to a particular document. Also called "find similar."

Recall: Related to precision, this is the degree in which a search engine returns all the matching documents in a collection. There may be 100 matching documents, but a search engine may only find 80 of them. It would then list these 80 and have a recall of 80%.

Relevancy: How well a document provides the information a user is looking for, as measured by the user.

Search Engine: The software that searches an index and returns matches. Search engine is often used synonymously with spider and index, although these are separate components that work with the engine.

Spider: The software that scans documents and adds them to an index by following links. Spider is often used as a synonym for search engine.

Stemming: The ability for a search to include the "stem" of words. For example, stemming allows a user to enter "swimming" and get back results also for the stem word "swim."

Stop words: Conjunctions, prepositions and articles and other words such as AND, TO and A that appear often in documents yet alone may contain little meaning.

Thesaurus: A list of synonyms a search engine can use to find matches for particular words if the words themselves don't appear in documents.

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