Hibernation means - An inactive, dormant, sleeplike state, in which the total funtions of systems though inactive, are preserved
Now,
In windows you have a special in built utility that allows to hibernate. hibernation allows all of your work to be saved as it is. It will stop the process,But keeo the window open .

For example, Suppose you are working in some heavy duty softwares which will take lots of time to save and somehow you need to shut your computer, This means you will have to loose that work. Hibernation will overcome this problem.
Try this: open two three notepad windows .. write some garbage in it, dont save it. Now if normally you shut the windows, these will be lost but if you click on hibernate and then shut down , you will get everything as it is.. on the screen ..........