The Free On-line Dictionary of Computing (30 December 2018):

US-ASCII

    The 7-bit version of ASCII, which preceded (and
   is the basis for) 8-bit versions such as Latin-1, MacASCII
   and later, even larger coded character sets such as Unicode.

   US-ASCII is defined in Standard ANSI X3.4-1986,
   "US-ASCII. Coded Character Set - 7-Bit American Standard Code
   for Information Interchange".

   (1998-10-18)