My understanding is that, most of the time, Standby is either a state (S1) where the caches are cleared and the CPU stops operating but power to the CPU and RAM continues, and the hard drives and video are suspended; or else a state (S3) in which the RAM power continues but everything else is powered down. S3 is also called "suspend to RAM" (STR). Hibernation is a state (S4) where RAM is saved to the hard drive and powered down also. Thus, hibernation is also called "suspend to disk." S4 is pretty close to being entirely off.
I couldn't name the states (that is truly admirable ) but a simpler version is: standby turns most of ur computer off and saves the current situation in RAM - good=fast recovery; bad=if lose power then everything is lost. hibernation saves everything to disk and turns the power off "completely" - good=loss of power can't hurt you; bad= slower power up. Both are more ecologically sensitive than leaving your pc turned on.
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