Hard Reset is a reboot on iphone, ipad or ipod to fix some problems, but different from the normal way. but with the same purpose.
Normal way to reboot the iphone, ipad or ipod. is pressing the power button / for a few seconds, until the appearing "Slide To Power Off".
Well, if you find you are having problems such as springboard crash or freeze as mentioned above, you should do a hardreset as initial actions to fix your problem.
How to Hard Reset Your iPhone, iPad, iPod
Step 1: Press the power/sleep button and home button at the same time, for a few seconds.
Step 2: The screen of the iPhone, iPad, your iPod will be dark, but you have to keep holding down the power/sleep and home buttons until a few seconds.
Step 3: If your iPhone, iPad or iPod you will re-display the Apple logo, release the power button and home. This means you have successfully done hardreset.
Step 4: Do not panic, because it takes a few seconds to load from the Apple logo to the main screen. This is normal.
Actually, this way can fix some problems on your iphone, ipad or ipod, but for now just a case example springboard crash or freeze. because it is the most common.
This method does not delete the app, song or settings on your iphone, ipad or ipod .