An #undef could be used to deal with a macro that is previously defined elsewhere, such as in a header file. It's possible that there are conflicting references to the named macro. It might be a macro in one place and a function in another.
In this case, it was determined that whatever is being read is simply too long to be a word, so it is reading until it ...
@DinoCoderSaurus is right.
See also 403 Forbidden / permissions / chmod -- the definitive guide on the CS50 Reddit, for details on the minimum required permissions for different types of file.
It's 711 for directories (unless you want Apache2 to generate a dynamic index when there is no index.html or index.php provided, then it's 755).
It's 644 for ...