The Master Cleanse is a diet that is usually done from anywhere between 10 and 30 days, and is meant to detox a person's body and help them lose weight fast.
Every morning a person must drink a saline solution of warm water and sea salt. Then the only thing the person can ingest for the rest of the day is a mixture of water, lemon juice, cayenne pepper and maple syrup.
The person can also have a cup of laxative tea at night. This process is to be repeated every day until the completion of the diet.
The diet is not recommended for people with health ailments, and it's suggested the person stops if they feel overly fatigued or weak.
The diet is actually meant to detox a person's body, it's not meant as a primary form of weight loss, although it does cause the dieter to lose weight. Most likely, since the weight is lost so fast, the person will gain the weight back quickly after the diet is finished.