Doctor is a title for graduate students studying for a doctorate, and it can also be used to address people who have obtained a doctorate. In foreign countries, it refers to people who have obtained doctoral degrees, while in China, doctoral students are also called so-and-so doctors.
Among the three levels of bachelor, master and doctor, doctor is the highest level.
A master's degree is a postgraduate degree between a bachelor's degree and a doctorate. A master's degree usually symbolizes the ability to think independently according to his concentration and research field.