Major depression, also known as clinical depression or unipolar depression, is classified as a type of affective disorder (also called mood disorder) that goes beyond the day's ordinary ups and downs.

Depression involves the body, mood and thoughts. It can affect and disrupt eating, sleeping, or thinking patterns, and is not the same as being unhappy or in a "blue" mood. It is not a sign of personal weakness or a condition that can be willed or wished away.

Children with a depressive illness cannot merely "pull themselves together" and get better. Treatment is often necessary and, many times, crucial to recovery.