The simple definition that my doctor gave me:
Celiac Disease is a disease of the intestines and digestive track. Over time, without going on a gluten-free diet, the intestinal track will deteriorate and surgery will be required. Celiac Disease causes a lot of pain in the stomach area as well as other health issues. In the past, many doctors diagnosed people with IBS (irritable bowel syndrome) when in actuality it was Celiac disease.
Gluten Sensitivity is most often caused by an outside factor such as a contact virus that in time causes the immune system to fight against itself. This is called an autoimmune disease. Gluten Sensitivity is rare and normally does not cause intestinal issues. Most times this autoimmune disease shows up on the skin and causes much discomfort due to excessive itching and blistering of the skin and most often is on the extremities and stomach area. Gluten Sensitivity is difficult to diagnose as it appears to be other diseases such as shingles or poison ivy. By eating a gluten-free diet the outward issues lessen and some studies have shown that over a three to four year period of a gluten-free diet, gluten may again be eaten in small quantities. These studies are fairly new and not 100% tested over a large population or time frame. If a person with Gluten Sensitivity does not follow a gluten-free diet, it can lead to Celiac Disease.