What is the biggest organ in the human body?

The skin is often known as "the largest organ of the human body". This applies to exterior surface, as it covers the body, appearing to have the largest surface area of all the organs. Moreover, it applies to weight, as it weighs more than any single internal organ, accounting for about 15 percent of body weight. For the average adult human, the skin has a surface area of between 1.5-2.0 square meters, most of it is between 2-3 mm thick. The average square inch of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand nerve endings.

https://en.wikipedia.org/wiki/Skin

The question does ask for "in" the human body which some may argue would exclude the skin.

The liver would be the second largest human organ and is unquestionably "in" the body.

http://curezone.com/forums/m.asp?f=73&i=749

"The skin is often known as the largest organ of the human body. This applies to exterior surface, as it covers the body, appearing to have the largest surface area of all the organs. Moreover, it applies to weight, as it weighs more than any single internal organ, accounting for about 15 percent of body weight. For the average adult human, the skin has a surface area of between 1.5-2.0 square meters (8-10.8 sq.ft.)."

https://en.wikipedia.org/wiki/Skin#See_also

The largest internal organ is the liver. It is also the heaviest organ, with an average of 1.6 kilograms (3.5 pounds). The largest external organ, which is also the largest organ in general, is the skin.

https://en.wikipedia.org/wiki/Largest_body_part