This line shows the OS family and if available; it also shows the OS generation (Linux 2.4.x, for instance). When Nmap cannot narrow down the generations, multiple OSes can be listed, divided by a pipe symbol. If Nmap finds too many OS families, it will omit this line. When there are no perfect matches for the OS family, Nmap adds an accuracy percentage (where 100 percent is a perfect match) after each possible candidate. If Nmap finds no close matches to fingerprints, the line is omitted.