Private Room, One's Own Room
noun
An individual room just for you is your own private room. How nice!
こしつ
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
カフェで個室を予約して、友達とゆっくりおしゃべりを楽しみました。
I reserved a private room at a cafe and enjoyed a leisurely chat with my friends.
トイレの個室って、小さなカメラが付けられてることがあるので、気をつけてね！
Toilets in individual stalls sometimes have small cameras installed, so be careful!
ジムに行ったら、ラッキーなことに個室のトレーニングエリアが空いていました。
When I went to the gym, luckily the private training area was available.