Depression is a medical condition where someone feels deeply sad, hopeless, or empty for weeks or months at a time, making it hard to enjoy things they usually love or even to get through ordinary days. Unlike feeling sad after something disappointing happens (which everyone experiences), depression doesn't go away quickly and may have no clear cause. Someone with depression might struggle to sleep, lose interest in friends and activities, feel exhausted all the time, or have trouble concentrating in school.

Depression is an illness that affects the brain's chemistry, similar to how diabetes affects the body's ability to process sugar. It's not something people can just “snap out of” through willpower alone, and it's not anyone's fault. Doctors and therapists can treat depression effectively with counseling, medication, or both. Many successful people throughout history have dealt with depression, including Abraham Lincoln and Winston Churchill, and have gone on to accomplish remarkable things.

The word can also mean a shallow dip or hollow in a surface, like a depression in the ground where water collects after rain. In economics, a depression is a severe, prolonged downturn. The Great Depression of the 1930s was a period when many businesses failed and millions of people lost their jobs, creating widespread hardship across the United States and the world.