Can you explain to all of us what a national security letter is, and what it allows? I'll provide some helper information to get the ball rolling (see page 42)

Can you explain to all of us what a national security letter is, and what it allows? I'll provide some helper information to get the ball rolling (see page 42)[1] [1]https://www.intelligence.gov/assets/documents/702-documents/statistical-transparency-report/ASTR_CY25.pdf https://www.intelligence.gov/assets/documents/702-documents/... All the other prime suspects are in the report too for the curious.