This is the 227th most frequent Japanese word.
専門
"Specialty" or "expertise."
The word '専門' is used here to describe a field of professional or academic specialty.
彼の専門はコンピュータサイエンスです。
His specialty is computer science.
In this sentence, '専門' is utilized to refer to a professional who has expertise in a specific area (as part of '専門家').
専門家に相談しましょう。
Let's consult a specialist.
Here, '専門' is being used as part of an adjective ('専門的な') to denote something that involves specialized knowledge or methods.