To reboot a computer is to cause it to shut down and then immediately boot again. The reboot command is part of the halt package, used to reboot the computer. It is generally used on its own except in special cases. The command is typically used by itself; a simple
on a command line will cause the computer to reboot.
Other ways of rebooting are using the command:
shutdown -r n
This will cause the computer to reboot in n seconds. 'now' can also be used in place of a number for n.