Weight loss refers to the reduction of the total body mass, either due to a mean loss of fluid, body fat, or lean mass. Generally, it occurs when an individual is in a state of negative caloric balance, where they are burning more calories than they are consuming. This can be achieved through a healthy diet, regular physical activities, or medically supervised programs. Unintentional weight loss can also be a sign of underlying medical conditions like diabetes, cancer, or malnutrition. It's always a good idea to consult with a healthcare professional or dietitian before embarking on significant weight loss.