This is the 4111th most frequent Russian word.
политолог
A political scientist.
In this sentence, 'политолог' refers to the profession of being a political scientist.
Он работает политологом в университете.
He works as a political scientist at the university.
In this instance, 'политолог' identifies a person, specifically an expert in political science, present at the conference.
На конференции выступал известный политолог.
A well-known political scientist spoke at the conference.
Here, 'политолог' is used to describe an academic professional or expert to whom the students directed their questions.