Metonymy is a figure of speech in which a concept is referred to by the name of something closely associated with that thing or concept.
The Pentagon is the headquarters building of the United States Department of Defense, and is a common metonym used to refer to the U.S. military and its leadership.
Fleet Street (where most British national newspapers previously operated) is used as a metonym for the British press.
A figure of speech or rhetorical figure is a word or phrase that intentionally deviates from ordinary language use to produce a rhetorical effect. Figures of speech are traditionally classified into schemes, which vary the ordinary sequence of words, and tropes, where words carry a meaning other than what they ordinarily signify.
Whitehall is a road in the City of Westminster, London used synecdochically to refer to the entire UK civil service, as many government departments are nearby.