Depression is a mental state characterized by low mood and a lack of interest in activities. It impacts over 280 million people globally, about 3.5% of the population. Depression influences a person's thoughts, behavior, feelings, and overall well-being, often leading to a loss of motivation and reduced enjoyment in activities that once brought pleasure.

Depressed mood can be a symptom of mood disorders such as major depressive disorder and dysthymia, a normal reaction to life events like losing a loved one, or a symptom of some physical diseases and side effects of certain drugs and treatments. Common symptoms include sadness, difficulty thinking and concentrating, changes in appetite, and altered sleep patterns. Those experiencing depression might feel dejected or hopeless and may have suicidal thoughts. Depression can be short-term or long-term, varying in duration and severity.