Digital twin technology evolved initially for production and engineering with Industry 4.0. But now it has entered into various fields like healthcare, aviation, etc. The digital twin models the state of a physical entity or process. The DT continuously predicts the status of defects or failures by closed loop optimization. Due to big data storage capabilities, data fusion algorithms, and artificial intelligence algorithms, DTs are capable of assessing any hidden patterns or unknown correlations, and with self-healing mechanisms, predictive maintenance approach is used to overcome them. In the healthcare applications, DTs of patients and medical devices virtually replicate the patient's physical characteristics or changes in body for correct diagnosis and treatment.