A learning disability or processing disorder which causes a person to not be able to recognize words that are misspelled as easily as a person who does not have it. Also people with dyslexia commonly have difficulty reading changing words around and adding them in where they aren’t. People with dyslexia are by no means stupid, in fact sometimes they are much smarter or more creative since a different part of their brain is more developed than the part that deals with language. People recently have started using dyslexia as an insult or otherwise just to justify things they've done backwards or words they’ve misspelled, but it is an actual disorder that many people have.
I was diagnosed with dyslexia in second grade when my teachers noticed my odd reading habits and inability to recognize the difference between the letters b and d when I spelled things.
We knew to test my brother for dyslexia in pre-k when he spelled his name completely backwards, nhoj, on a homework assignment.