1)...Used to be, perhaps 25yrs ago, just a radiological diagnosis seen on Ba.swallow. Some time later it was then to be seen that it was indeed a clinical entity. Then, when endoscopy came into play, the lower part of the oesophagus was seen to be abnormal and this was confirmed by biopsy.
It was argued that acid was regurgitating backwards through the valve causing this change.
Barretts oesophagus in itself is not pre-maignant, but in the last decade it has been seen that some cancers can occur in this region.
2) I would bet that nobody outside of the medical establishment has heard of this condition, except those who have it or have heard of soneone who has it.