Glomar Response-Office of Government Information Services
"In some cases, admitting that records exist or do not exist would reveal an exempt fact (for instance, whether an agency was conducting a criminal probe of an individual or entity). To protect that fact, an agency may choose to neither confirm nor deny the existence of records in response to a FOIA request. This is called a “Glomar response” (see below for the background of this term).Glomar responses are generally used in response to FOIA requests for records pertaining to national security or criminal law enforcement matters. However, a Glomar response may be appropriate in connection with any of FOIA’s nine exemptions."