[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.