This is the 105th most frequent Korean word.
중이다
"중이다" means "to be in the middle of" or "to be in the process of."
Here, 중이다 is used to indicate that the subject is currently in the process of thinking.
다른 일을 할 수 없어요, 생각 중이에요.
I cannot do other tasks; I am thinking.
In this case, 중이다 is utilized to show the present engagement in studying.
그는 공부 중이어서 방해하지 않으려고 노력했어요.
He was studying, so I tried not to disturb him.
In this sentence, 중이다 is used to express that the subject is currently engaged in an activity, specifically a meeting.