This is the 17076th most frequent Korean word.
생각이다
"It is an idea" or "to think."
This usage of '생각이다' indicates a plan or intention.
오늘은 집에 있을 생각이다.
I plan to stay home today.
Here, '생각이다' expresses an opinion or a considered thought.
그 문제를 푸는 데 시간이 필요할 생각이다.
I think solving that problem will require time.
In this sentence, '생각이다' is used for a belief or anticipation.