"Sources and methods" seems to be an official CIA/NSA terminology to talk about the main categories things that whistleblowers were not supposed to whistleblow.
It came to Ciro Santilli's attention in the Reality film about Reality Winner, and are words she apparently used extensively and which are quoted e.g. at www.theguardian.com/us-news/2022/jul/25/reality-winner-leaked-file-on-russia-election-hacking-because-public-was-being-lied-to
The term is more broadly used however outside of the NSA, e.g. it is also present on this website which talks about the CIA 2010 covert communication websites fiasco.
Edward Snowden in 2013
. Source. From the film Prism, during interview with reporter Glenn Greenwald.
Articles by others on the same topic
The National Security Agency (NSA) is a U.S. government agency responsible for signals intelligence (SIGINT) and information assurance. Established in 1952, the NSA is part of the Department of Defense and is tasked primarily with monitoring and collecting foreign communications and intelligence data to ensure national security.