The option description:
Gives the chance to specify an optical disk drive (CD, DVD or Blu-ray) on which first of all it is necessary to search for an operating system. The option is actual, when such drives are connected to the computer some.
In most cases at a choice of this option (pushing it of a key [<Enter>]) you get to the additional menu where it is already possible to select the order of inquiry of optical disk drives immediately.
Other options identical to destination: