Synesthesia: Noun – The production of a sense impression relating to one sense or part of the body by stimulation of another sense or part of the body,
What does that mean? Simply stated, the brain of a synesthete confuses one sensory experience for another, and the result of that confusion is the manifestation of a sensation that does not correspond to the experience. For example, one of the most common forms of synesthesia is that of Grapheme -> Color Synesthesia, where numbers or letters appear to the synesthete as being colored when they are not. These people actually see a color along with the number or letter when they view it – it’s as though the number or letter has a colored aura.