Depression is a mental health disorder marked by persistent sadness, emptiness, and a loss of interest in activities. Symptoms include changes in appetite or sleep, fatigue, difficulty concentrating, feelings of worthlessness, and physical issues like headaches. Severe cases can lead to social withdrawal and suicidal thoughts. Diagnosis is conducted by mental health professionals through clinical interviews and standardized scales, requiring at least five symptoms over two weeks. A thorough evaluation also considers medical history to rule out other conditions. Tools like the Patient Health Questionnaire-9 may be used to assess severity.