What is the difference between 2.5D and 3D design

Nowadays.Smart phones have been poplar with the 2.5D screen design,such as iPhone,Xiaomi note.When buying a screen protector.People will also use 2.5D screen protector as the first choice.The problem is what does the 2.5D screen mean?And What's the difference between 2.5D and 3D screen protector?

Generally speaking, the 2.5D screen refers to some smart phones that use the 2.5D glass screen. As early as 2011, Nokia launched the first 2.5D screen mobile phone: Nokia N9.

In short, the 2.5D screen means that the edge of the screen protector use the 2.5D arc design,but the bottom screen itself is still plain. The follow picture is a close-up of the iPhone 6 on the 2.5D glass screen.

In short, the ordinary screen is that the screen is a pure plane without any arc design; the 2.5D screen is a plane in the middle, but the edge is an arc design; the 3D screen, both in the middle and the edge, is an arc design