Lysdexia

The transposition of letters or words, specifically in relation to written electronic communications, such as Email or web pages.

Some examples, such as the typing "teh" instead of "the" are so well known that they have become commonly known and used deliberately.

A wordplay (technically an anagram) on dyslexia. It is generally symptom of attempting to type quickly rather than the condition of dyslexia. As such, it is far more common in a medium such as a chat room, where participants perform minimal editing or proof reading in order to respond in a timely manner.