According to Dictionary.com, a "summary" is a noun that means a broad and generally brief account of previously stated facts. A summary of a novel, for example, would quickly and accurately describe the book's entire plot from beginning to end.
"Summary" is also used, though less commonly, as an adjective meaning an act performed quickly and without formality or ceremony. A summary execution, for example, would be one performed on the spot without any of the typical accompanying observances or rituals. "Summary" first appeared in English in the 15th century, and is derived from the Middle Latin "summaries," meaning something of or pertaining to the sum or substance. The connotation of a summary being performed promptly emerged in the early 18th century.