DETCOM Program

The DETCOM Program (also "Det-Com," "Detcom"), along with the COMSAB (or "COMmunist SABotage") Program formed part of the "Emergency Detention Program" (1946–1950) of Federal Bureau of Investigation (FBI). As FBI historian Athan Theoharis described in 1978, "The FBI compiled other lists in addition to the Security Index. These include a "Comsab program" (concentrating on Communists with a potential for sabotage), and "Detcom program" (a "priority" list of individuals to be arrested), and a Communist Index (individuals about whom investigation did not "reflect sufficient disloyal information" but whom the bureau deemed to be 'of interest ... '.")
Secrecy.
Long-time FBI head J. Edgar Hoover wanted the program to remain secret from the public: 
He thus instructed his top agents that "no mention must be made in any investigative report relating to the classifications of top functionaries and key figures, nor to the Detcom or Consab Program, nor to the Security Index or the Communist Index. These investigative procedures and administrative aids are confidential and should not be known to any outside agency."
Description.
Most sources take "DETCOM" to stand for "DETain [as] COMmunist" (bolding added):
List.
By 1951, the FBI had formalized the program: "Forms beginning in 1951 included a space labeled "Tab for Detcom" and "Tab for Comsab." ("Tab: To place in a special category in an FBI list such as Security Index, e.g., to tab an SI subject "Detcom.") People listed on DETCOM were referred to as "tabbed for DETCOM."
Americans "tabbed for DETCOM Program" included: