Report Of The Commission On Protecting And Reducing Government Secrecy, 1997:

"Publicly acknowledged programs are considered distinct from unacknowledged programs, with the latter colloquially referred to as "black" programs because their very existence and purpose are classified. Among black programs, further distinction is made for "waived" programs, considered to be so sensitive that they are exempt from standard reporting requirements to the Congress. The chairperson, ranking member, and, on occasion, other members and staff of relevant Congressional committees are notified only orally of the existence of these programs.

There are approximately 150 DoD-approved SAPs (the exact number is classified and others have been created but not yet formally approved), down from 200 in the late 1980s, and roughly 300 SCI compartments, compared with an estimated 800 in the late 1980s. These numbers, however, do not include the many subcompartments, perhaps best termed "SAPs within SAPs," that further limit the extent to which personnel have access to various parts of the same program."

https://fas.org/sgp/library/moynihan/chap2.html

https://fas.org/sgp/library/moynihan/index.html Full Report