The Wiki summary here is good, and you can go read other sources if you'd like.
I have recently established a web site containing a summary of what actually will be done within the purview of our research.
The Overview is a summary of a longer classified document (unavailable until WikiLeaks or the Washington Post releases it).
early 15c., from Medieval Latin summarius "of or pertaining to the sum or substance," from Latin summa "whole, gist" (see sum). Sense of "done promptly" is first found 1713. The noun meaning "a summary statement or account" is first recorded c.1500, from Latin summarium "an epitome, abstract, summary," from summa "totality, gist."