What does glass separating from iphone 5s mean?

Well i'm about to buy a iphone 5s thats says that the glass is actually separating from it, i don't know what that means but i messgaed them and they have not got back to me

It means that the screen is screwed and you'll soon need to replace it.

Unless you have experience of diagnosing and fixing faulty phones, and accept the risks that sometimes what you buy will have additional faults or be unfixable, then steer well clear. There are plenty of fully functional examples around; you don't need to waste money on someone else's junk.

That's not good. It means that the front panel is literally coming off. This phone is all but broken, buy it only if you need a part from it.

It is what it sounds like. The glass display is moving apart from the unit.