Gracefully  restarts  the  Apache httpd daemon. If the daemon is not running, it is started. This differs from a
normal  restart in  that  currently  open  connections  are not aborted. A side effect is that old log files will  not
be  closed  immediately. This  means that if used in a log rotation script, a substantial delay may be necessary to ensure that  the  old  log  files  are closed before processing them. This command automatically checks        
    the configuration files as in configtest before initiating  the restart  to  make sure Apache doesn?t die.
This is equivalent to apachectl -k graceful.
( excerpt from manual page of apachectl )
Actually it sends a SIGUSR1 for a restart. The USR1 or graceful signal causes the parent process to advise the children to exit after their current request (or to exit immediately if they're not serving anything). The parent
re-reads its configuration files and re-opens its log files.As each child dies off the parent replaces it with a child
from the new generation of the configuration, which begins serving new requests immediately.

It sends a SIGUSR1 for a restart, and starts the apache server if it's not running.