This is the 7695th most frequent Japanese word.
博士
Doctor; PhD holder.
In this instance, '博士' is used as a respectful title for addressing someone who holds a doctoral degree.
博士、これはいかがですか？
Doctor, how about this?
In this sentence, '博士' is used to denote a person who has obtained a doctoral degree in the field of physics.
彼は物理学の博士だ。
He is a doctor of physics.
Here, '博士' refers to the academic degree itself, representing the goal of achieving Ph.D. status.