Answer: During routine, legal surveillance of foreign targets, names of Americans occasionally come up in conversations. Foreigners could be talking about a U.S. citizen or U.S. permanent resident by name, or a foreigner could be speaking directly to an American. When an American's name is swept up in surveillance of foreigners, it is called "incidental collection." In these cases, the name of the American is masked before the intelligence is distributed to administration officials to avoid invading that person's privacy.

Unless there is a clear intelligence value to knowing the American's name, it is not revealed in the reports. The intelligence report would refer to the person only as "U.S. Person 1" or U.S. Person 2." If U.S. officials with proper clearance to review the report want to know the identity, they can ask the agency that collected the information perhaps the FBI, CIA or National Security Agency to "unmask" the name.

Unmasking requests are common, according to Michael Morell, former CIA deputy director and host of "Intelligence Matters" podcast.

"Literally hundreds of times a year across multiple administrations. In general, senior officials make the requests when necessary to understand the underlying intelligence. I myself did it several times a month and NSA adjudicates the request. You can't do your job without it," he said.

Morell emphasized that unmasking is not the same as declassification. "When a name is unmasked, the underlying intelligence to include the name remains classified so leaking it would be a crime."

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Q&A: What is 'unmasking'? - The Southern