uspend does not turn off your computer. Suspend puts everything into RAM, and shuts off processes except to maintain memory, and detect start-up triggers. It stops computer operations of all applications and peripherals, and puts the machine into a low-power mode. If the battery runs flat or the computer switches off, the current session and all unsaved changes will be lost. Various triggers can resume the machine state, by pressing a key or pressing and releasing the power button. Sometimes called 'sleep mode'.
Hibernate saves the contents of computer memory to the swap file on hard disk, powers off and shuts the machine down. When resuming, the saved state is restored to RAM. On machine by power up, the kernel reloads the memory contents from swap. To resume your previous session, press the power button, similar to a cold boot. No power is used when the computer is hibernating.
Resume brings the computer out of power saving mode and back to normal operation to continue with your previous work session. Documents open along with applications will start from last saved session. To resume from suspend press a key or click the mouse. To resume from hibernate, press the power button on the computer.
Reboot flushes the cache to disk. It logs entries in user account files. Kills all running processes. Reruns start up scripts.
Shut Down turns the computer off, without saving the current state. Current session is not resumed on next start-up. No power is used when the computer is shut down.