What is an “invisible illness?”

The Wikipedia definition is: (Invisible illnesses) or disabilities are chronic illnesses, and conditions that significantly impair normal activities of daily living. In the United States, 96% of people with chronic medical conditions show no outward signs of their illness, and 10% experience symptoms that are considered disabling.

I have an invisible illness, so I can give a first-hand explanation…With my Cystic Fibrosis, I show only one or two outward signs that I am “sick.” I cough a lot, and I am rather skinny. However, if you didn’t realize what that meant, as in if you weren’t already familiar with CF symptoms you wouldn’t know in any way that I was chronically ill, hence invisible illness.