What is the meaning of the words with underline in a man page?

Solution 1:

Most underlined words in man pages are for emphasis. Its is not a hyperlink .

Solution 2:

also from man man page

   italic text        replace with appropriate argument.
   [-abc]             any or all arguments within [ ] are optional.
   -a|-b              options delimited by | cannot be used together.

   argument ...       argument is repeatable.
   [expression] ...   entire expression within [ ] is repeatable.

   Exact rendering may vary depending on the output device.  For instance,
   man will usually not be able to render italics when running in a termi‐
   nal, and will typically use underlined or coloured text instead.