Hibernate or suspend to disk in computing can be known as powering down computer and retaining its state. In the hibernate state, the operating system save the contents of RAM into a hard disk or non-volatile things then power down the machine.
Sometimes when we seriously working on something suddenly a serious things occurs (like have to move to another place, need to do something important, etc.). Of course in this moment we doesn’t want to lose what we have done and have to keep our working state. When this things happen, we can use the hibernate function to retain our works which is still in RAM into a hard disk. After the serious things is finished we can get back to work and all the conditions of the computer will return exactly at the point of the hibernation.