In information retrieval, a measure of the effectiveness of a search, expressed as the ratio of the number of relevant records or documents retrieved in response to the query to the total number of relevant records or documents in the database; for example, in a database containing 100 records relevant to the topic "book history," a search retrieving 50 records, 25 of which are relevant to the topic, would have 25 percent recall (25/100). One of the main difficulties in using recall as a measure of search effectiveness is that it can be nearly impossible to determine the total number of relevant records in all but very small databases. Compare with precision. See also: fallout.


From ODLIS, Online Dictionary of Library and Information Science by Joan M. Reitz
http://lu.com/odlis/odlis_c.cfm