Updated 2021.03.17
Burn in is more properly known as "uneven phosphor wear".
What causes burn in?
CRTs (or plasma phosphors) "wear/age" as they are used. If the same part of the TV is "hit" with the same image for long periods of time, it will "wear" differently from the other parts of the CRT that are being "hit" with varying images.
After a while, this results in uneven phosphor wear, or "burn in". You will be able to see the image that was 'static' on your TV - for example, a logo...
FAQ - Burn In & Break In.
Burn in is more properly known as "uneven phosphor wear".
What causes burn in?
CRTs (or plasma phosphors) "wear/age" as they are used. If the same part of the TV is "hit" with the same image for long periods of time, it will "wear" differently from the other parts of the CRT that are being "hit" with varying images.
After a while, this results in uneven phosphor wear, or "burn in". You will be able to see the image that was 'static' on your TV - for example, a logo...
FAQ - Burn In & Break In.