The null device is a special file that discards all data written to it, but reports that the write operation succeeded.
It is often used to hide the output (or error output) of a command.
e.g.
SomeCommand >nul
Nul provides no data to any process that reads from it (yielding EOF immediately)
For more examples see the redirection page.
“Never mistake activity for achievement.” ~ John Wooden
Related:
PRN - redirect to the printer LPT1.