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What does “--” (double-dash) mean?
What does '--' (two dashes) mean with association to Linux files and directories.
I've found something else but not too sure if it is correct and relates to the same thing. "Another convention is to use '--' (two dashes) to indicate the end of flags, and the beginning of file names."
I'm not sure if you mean - or --, so here's some information about both:
- is a shorthand that some programs accept to refer to STDIN, the standard input of the program. That is, in a pipeline like echo foo | cat - (although - is actually unnecessary in this instance), cat receives "foo" and a newline as its input from STDIN.
-- indicates the end of arguments. In programs that deal with files, this often means that what follows will only be filenames, and not, say, command-line options. In such an instance it is used to try and get around filenames that look like options (for example, if you have a file named -e and an the program also accepts a -e argument). Another way to get around this is to do something like command ./-e, which is actually more compatible across programs as it doesn't require the underlying program to implement handling --.
-has a meaning too when used as a filename (it typically means stdin/stdout), but the second paragraph is clearly talking about--, so I'm not sure which he actually wants