This is the 71st most frequent Japanese word.
部
"部" means "department," "section," "club," or "part."
Here, "部" is used to mean 'club' or organized group as part of an institution or activity (a tennis club in this context).
私はテニス部に入っています。
I am a member of the tennis club.
In this sentence, "部" appears as part of the word "部屋", meaning 'room'. It suggests a division or part of a building.
部屋の掃除をしました。
I cleaned the room.
Here, "部" means 'department' within an organization, specifically referring to the Sales Department.