The Free On-line Dictionary of Computing (19 January 2023):

EOF

   End Of File

   1. The out-of-band value returned by C's sequential
   character-input functions (and their equivalents in other
   environments) when end of file has been reached.  This value
   is -1 under C libraries postdating V6 Unix, but was
   originally 0.

   2. The keyboard character (usually control-D, the ASCII EOT
   (End Of Transmission) character) that is mapped by the Unix
   terminal driver into an end-of-file condition.

   [Jargon File]

   (1995-01-18)


The Jargon File (version 4.4.7, 29 Dec 2003):

EOF
 /E·O·F/, n.

    [abbreviation, ‘End Of File’]

    1. [techspeak] The out-of-band value returned by C's sequential
    character-input functions (and their equivalents in other environments)
    when end of file has been reached. This value is usually -1 under C
    libraries postdating V6 Unix, but was originally 0. DOS hackers think EOF
    is ^Z, and a few Amiga hackers think it's ^\.

    2. [Unix] The keyboard character (usually control-D, the ASCII EOT (End Of
    Transmission) character) that is mapped by the terminal driver into an
    end-of-file condition.

    3. Used by extension in non-computer contexts when a human is doing
    something that can be modeled as a sequential read and can't go further. “
    Yeah, I looked for a list of 360 mnemonics to post as a joke, but I hit EOF
    pretty fast; all the library had was a JCL manual.” See also EOL.