To correctly diagnose and treat a double chin takes care and understanding of the structure and function of the tissues.
In common usage we normally mean a roll of pinchable fat under the skin of the chin. In addition, there can be poor definition of the jawline and often this is accompanied by a short chin.
Do I Have a Double Chin?
Not everyone who thinks they have a double chin, has any fat that can be removed, their profile is due to the shape of the muscles of the neck. This cannot be changed to a great degree.
Some patients do indeed have a double chin, the skin is firm and tight. Those patients can have any treatment to remove the fat.