Recall

The portion of relevant documents that were retrieved when compared to all relevant documents.

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%.

For a query, recall means the ability to retrieve as many documents as possible that match or are related to a query. Recall may be improved by linguistic processing such as lemmatization, spell-checking, and synonym expansion.