Looking up the word confidential in the dictionary, we find that it means secret or private. However, the word confidentiality means so much more. Confidentiality is more about how one conducts themselves on a professional level.
In the medical field, confidentiality is much more than keeping specific patient information secret; it is also about professionalism. In today's world many only know us through online chat rooms, online forums, Facebook, LinkedIn, etc. Thus, how we conduct ourselves in those venues is how we portray our ability to maintain confidentiality.
We all understand that one would never talk about a patient specifically, but how often do we see things like "I just don't know how Dr. Munster deals with all those neurotic patients he sees every day," or "Dr. Repeat said that over and over and over again," or "I just did a report and the patient weighed 600 pounds!" While these examples may not be a true breach of confidence, they definitely display a lack of confidentiality.
This type of behavior reflects badly on the person stating these things. I can assure you that employers frown upon such behavior and take notice. Thus, the easiest way to not have to defend your behavior at some point is to maintain confidentiality/professionalism at all times.