I'm not so certain that the issue is the definition of the term normal, so much as it is the value (positive or negative) or association (healthy vs. unhealthy) the term implies in a medical or social context.
One of the most common reasons for blurry vision while wearing contacts is that your eyes are dry. Some people have a medical condition that causes dry eyes, called dry eye syndrome, but others' eyes are irritated by the contacts themselves.
If you have sudden blurry vision in one eye and are over 60, you may have developed a macular hole in the part of the retina where fine focusing occurs. Blurry vision also may be a symptom of a detached retina, eye herpes or optic neuritis (inflammation of the optic nerve), among other causes. Certain eye conditions and diseases can cause permanent loss of vision, so it's important to visit your eye care practitioner for diagnosis and prompt treatment.