What does the "Shadow/Burn Screen" of a smartphone mean?

Question

Android

I'm looking for smart on ebay. And I noticed that in many proposals indicate screen defects that do not affect functionality. Can you tell me what is the defect? I've highlighted the part I'm interested in:

This item is in Good Condition with some scuffs/ scratches on housing and screen please note these phones have Shadow/Burn Screen which is mostly visible on white background and does not effect any functionality of the phones. Fully Functional – Comes with generic box charging usb and adapter. - This item is GSM Unlocked will work worldwide (Compatible for GSM Carriers)” Will not work with Verizon, Sprint and Boost””

PS Do I understand correctly that this is a screen burn-in effect due to a long display of a static picture? Like in a window?

Answer 1

These are such dark stains, visible only on a white background, usually due to dust that got under the glass. I will add, burnout, as you suggested, is also possible. But it must be a very old smart.