This is the 7504th most frequent Japanese word.
入院
Hospitalization.
The word 入院 (hospitalization) is used here to explain the action/state of being admitted to a hospital for treatment.
私の祖父は先週入院しました。
My grandfather was hospitalized last week.
The word 入院 (hospitalization) in this sentence describes a period during which the individual is staying in the hospital.
入院している間、医者が彼を毎日診察しました。
While he was hospitalized, the doctor examined him every day.
The term 入院 (hospitalization) emphasizes the concept of being admitted to the hospital due to a health condition.