Sometimes I find in the source code files comments have quotation marks like these ,notice the ` :`help'``helpFor example, these are comments from GNU cat source code file, cat.c:  /* Plain cat.  Copies the file behind `input_desc' to STDOUT_FILENO.  */>  /* Select which version of `cat' to use. If any options (more than -u,     --version, or --help) were specified, use `cat', otherwise use     `simple_cat'.  */>/* Suppress `used before initialized' warning.  */While in other parts,  is used :  /* Determines how many consecutive newlines there have been in the     input.  0 newlines makes NEWLINES -1, 1 newline makes NEWLINES 1,     etc.  Initially 0 to indicate that we are at the beginning of a     new line.  The state of the procedure is determined by     NEWLINES.  */What does ` mean? and what is it used for?
Is there a difference between the quotes in `help',``help, 'help' and help?
documentation;comments
It's the result (habit) of someone using LaTeX - it doesn't mean anything.E.g., in LaTeX, ``hello there'' would result in hello there.If, however, you see as part of a shell script, the command within the backticks () is performed. E.g.,  $ echo `whoami`awesome-linux-accountname