What is the hard plastic frame going around the 4G iPod touch's screen?

There is a hard plastic frame that goes around my fourth gen iPod touch's screen and I seriously don't know what it is? The only reason I can tell it apart from my screen is because I dropped my iPod one day and that frame chipped but not the glass... Could it be the wifi antenna, because ever since, my wifi has been really messed up like losing connection but my other iPod is connected perfectly fine?