What is the term for when you think your fat but you are not?

The term for believing you are overweight or fat when you are not is often referred to as "body dysmorphic disorder" (BDD) when it is a severe and persistent condition. It can also be described as having a distorted body image or body image distortion. This perception can lead to significant emotional distress and affect one's self-esteem and mental health. It's important for individuals experiencing this to seek support from mental health professionals.