The Free On-line Dictionary of Computing (19 January 2023):
amp off(Purdue) To run in background. From the Unix shell "&" (ampersand) operator. [Jargon File] (1995-11-14) The Jargon File (version 4.4.7, 29 Dec 2003):
amp off vt. [Purdue] To run in background. From the Unix shell ‘&’ operator.