Short answers, pulled from the story.
A boilerplate spacecraft is a nonfunctional craft or payload that serves as a mass simulator for testing launch vehicle configurations. It allows engineers to test various sizes, loads, and handling characteristics without the expense of building a fully operational system.
NASA performed many tests using these mockups atop Saturn I rockets and Mercury spacecraft on Atlas rockets in the early 1960s. The first successful pad abort flight test occurred with a functional escape tower attached to a Mercury boilerplate on the 22nd of July 1959.
The conical section of the original capsule was constructed from steel sheets at the Norfolk Naval Shipyard facility. Historically, Mercury boilerplates were manufactured in-house by NASA Langley Research Center technicians prior to McDonnell Aircraft Company building the actual spacecraft.
BP-1227 was lost at sea somewhere between the Azores and Bay of Biscay in early 1969 before being recovered by Soviet fishing trawler Apatit. This specific unit served as part of the variety of Apollo boilerplates created by NASA including BP-6 which performed Pad Abort Test-1.
In January 1977, prototype orbiter Enterprise was delivered to Edwards Air Force Base in California for its overall test programme. During 1977, Enterprise was used in Approach and Landing Tests programme which encompassed mating the orbiter to Shuttle Carrier Aircraft.
Commercial spacecraft boilerplates emerged in the 2010s with Dragon Spacecraft Qualification Unit launched to orbit on the 4th of June 2010. The Cygnus Mass Simulator capsule was launched to orbit on the 21st of April 2013 on the maiden flight of Orbital Sciences Corporation Antares rocket.