Differential diagnosis refers to the determination of which of two (2) or more possible diagnoses is most appropriate for a client; the process of systematically ruling out alternative diagnoses.
Moreover, Differential diagnosis is the process of being able to differentiate one condition or disorder from another through the use of set diagnostic criteria. The term is based on a medical-disease model in which accurate diagnosis is believed to inform a clinician about effective treatments.
Other /More definition:
Differential diagnosis refers to the process of systematically ruling out alternative diagnoses.
Lexicon of Psychology - Terms, Treatments, Biographies,