Fats in the human body are primarily stored in adipose tissue. Adipose tissue is a type of connective tissue that consists of fat cells called adipocytes. These adipocytes store excess calories in the form of triglycerides, which are made up of fatty acids and glycerol.

Option 1, the epidermis, is the outermost layer of the skin and does not store significant amounts of fat. Option 3, the liver, plays a role in processing and metabolizing fats, but it does not primarily store them. Option 4, the epithelium, is a type of tissue that lines the surfaces and cavities of the body, but it is not primarily responsible for fat storage.

Therefore, the correct answer is option 2, adipose tissue.