hospital
A hospital is a place where sick people are looked after by doctors and nurses.
In British English, if you want to say that someone is in a hospital without mentioning which hospital they are in, you say they are in hospital.
I used to visit him in hospital.
She had to go into hospital for an operation.
American speakers do not say ‘in hospital’. They say in the hospital.
She broke her back and spent some time in the hospital.
In both British and American English, if you want to say that something happened in a particular hospital, you usually say at the hospital.
I was working at the hospital.