In Crohn disease (CD), there are some parts of the intestine that are healthy and there are some areas that are inflamed. Ulcerative colitis (UC), on the other hand, is continuous inflammation of the whole colon.

Explanation:

UC and CD are the two main forms of inflammatory bowel disease.
Both conditions affect the digestive tract and can occur at any age.
The causes could be environmental, genetic, or inappropriate body immune response to inflammatory triggers.
UC is limited to the colon whereas CD can occur anywhere between the mouth and the anus.
UC only affects the inner most lining of the colon, whereas CD can occur in all the layers of the bowel walls.

Sources:

crohn's disease vs ulcerative colitis - Google Search
Ulcerative Colitis vs Crohn's Disease - UCLA Center for Inflammatory Bowel Diseases - Los Angeles, CA (uclahealth.org)