Depression, also known as major depressive disorder, is a common and serious medical illness that negatively affects how a person feels, thinks, and acts. It is a mood disorder that causes persistent feelings of sadness and loss of interest, which can interfere with daily life. Depression is more than just feeling "down in the dumps" or "blue" for a few days; it is a serious mental illness that affects more than 20 million people in the United States. There are different types of depression, including major depressive disorder, persistent depressive disorder, perinatal depression, and seasonal affective disorder. Symptoms of depression can vary from person to person, but they may include persistent sad, anxious, or empty mood, feelings of hopelessness or pessimism, loss of interest or pleasure in hobbies and activities, decreased energy, fatigue, and changes in sleep patterns. It is important to note that depression is different from normal feelings of sadness or grief, and it is not a sign of weakness or a character flaw. Effective treatments and supports are available to help individuals with depression start feeling better, and seeking professional help is crucial for managing the condition.