What is difference between physical medicine n rehabilitation n physiotherapy?

A lot!: Physical medicine and rehabitation is a field and a medical specialty (physicians who have this specialty are called physiatrists). Physiotherapy or physical therapy is one modality used for rehabilitation. Physical therapists are the specialist and have specialized training (masters or doctoral degrees). They do hands on treatment that includes exercise and other manual techniques.

MD vs PT: Physical medicine & rehabilitation is a specialty of medicine, so that is a doctor of medicine. Physiotherapy is a clinical specialty of a therapist, physical therapist. Typically the doctor orders the type of therapy needed to be done and the therapist will actually work with you on this order of exercise. The two specialities are interlinked and work together.