In attention, a value is a content vector used in the weighted sum that produces an output. It can differ from the vector used to score relevance. section 15.3.1
Figure 15.6 Retrieving images from a database: the query is compared to a set of keys, and the match scores are used to rank values (images).
Photo retrieval offers an analogy: a query matches against keys, while the resulting scores rank the values—the photos being retrieved. section 15.3.1







