Dyslexia is a specific learning difficulty that primarily affects language. There are many different kinds of dyslexia: visual dyslexics have difficulty reading words or writing letters the correct way round (they may mistake 'b' for 'd', for example) whereas people with auditory dyslexia have trouble processing sounds and getting phonemes in the correct sequence when they try to write things down. Other difficulties associated with dyslexia include short-term memory problems, a weak attention span, and poor organisational skills.
Dyslexia is not a synonym for stupidity, as most dyslexics have high IQ scores. It is also not a made-up 'excuse', as MRI scans of dyslexic people have found that their brains are shaped differently to those of most people, with the language area in the right hemisphere being the same size as the language area in the left. (In people without dyslexia, the left language processing area is much larger than the one in the right hemisphere.)
Dyslexic people are often particularly gifted in art, music, sport, drama, or anything involving visual creativity. Some are also talented authors - the awardwinning poet Benjamin Zephaniah is dyslexic.
Examples of famous dyslexic people include Steve Redgrave, the Olympic athlete; Whoopi Goldberg, the Oscar-winning actress; and Albert Einstein, the genius who developed the Theory of Relativity. (People who say that 'dyslexia = stupid' are usually completely unaware that Einstein had the condition.)