Dyslexia is actually a term covering a range of learning disabilities, all involving a person having problems with language. Generally, dyslexia only refers to disorders that you are born with; if you acquire it later in life, it will be referred to as aphasia. (Although aphasia is generally thought of as affecting speech and comprehension of speech, it may also affect reading and writing). We do not yet have a good understanding of what causes dyslexia, nor how to treat it. Most treatment programs are essentially a form of "practice, practice, practice!"
Phonological dyslexia
- The main impairment is in pronouncing novel letter strings such as 'Blut'
- This is always a problem with the reading and comprehension of phonetic relations within words; if you are having problems moving your tongue into position to make words, you have apraxia, not dyslexia.
Surface dyslexics
Deep dyslexics
- The main impairment is semantic paraphasias such as pronouncing 'sympathy' as 'orchestra.' These semantic substitutions may be a comparatively minor symptom, but If this happens even once or twice during a reading session, it should be a red flag!
- People with deep dyslexia may not be able to read phonetically -- but may appear to read phonetically by first doing whole-word recognition, and then accessing the phonology.
- Cannot make rhyme judgments on words.
- Cannot read nonsense words.
It wasn't that long ago (the late 70s and throughout the 80s, basically) that dyslexia was a go-to disorder (in much the same way as autism and ADD/ADHD are today). If something was going wrong with a kid in school, 'dyslexia' was a socially acceptable and more-or-less generally understood disorder -- so we labeled kids as dyslexic left and right. Obviously, a diagnosis like this is not exactly comforting, but it's nice to be able to give a label to the problem.
Due to the vagueness of the simple term 'dyslexia', the general lack of testing to back up such a diagnosis, and the fact that it doesn't tell you much of anything about how to correct the problem, most educators are a little wary of the term these days; the broader term learning disability is often used in its place. Many cases of dyslexia might better be considered types of visual processing disorder. And moreover, many of the problems that were once attributed to dyslexia are now attributed to a lack of phonological awareness skills, which at least gives us clear preventive measures, i.e., read to your kids!
While it may be useful to claim that your child (or yourself) is dyslexic, be aware that this does not really tell anyone anything except that 'he has trouble reading'. If you have to deal with dyslexia on a practical level, you should identify specific problems and focus on overcoming those. The umbrella term dyslexia does not contain any real information on its own, and should be a starting point of a long and complicated explanation, not a pithy way to pigeonhole people.