Rosacea: Red skin disorder

Rosacea is a common skin condition that, if left untreated, can cause quite severe complications.

MY friend has been suffering from red patches on her face for a very long time. At first, she thought she was just flushed from the heat, but it persisted for a very long time. Then she thought she was going to develop pimples, but they never came on. Finally, she went to a skin doctor and she was told she has rosacea. I have never heard of this condition. What is it?