This is the 837th most frequent Japanese word.
大事
Important; valuable.
In this sentence, '大事' is used as an adjective to describe the importance of health.
彼女は健康が大事だと言っています。
She says that her health is important.
Here, '大事' is used to emphasize the significance of the meeting.
これはとても大事な会議です。
This is a very important meeting.
In this context, '大事' is used in a phrase to suggest cherishing or valuing something.