Psychotherapy is a for of treatment to help people feeling better about themselves and resolving problems. Usualy conducted by a trained mental health professional (whether psychiatrist or psychotherapist) in a one-on-one setting, although sometimes conducted in group as well.
Psychotherapy is done in many different ways, and may follow many different techniques, depending on the therapist's training.
Often referred to as "talk therapy", it has proven to be innefective in treating Body Integrity Identity Disorder, albeit there are no formal studies to prove it so, and we must rely on anecdotal evidence instead.
For more general information on psychotherapy, see: Wikipedia:Psychoterapy