This is the 4180th most frequent Japanese word.
上海
"上海" means "Shanghai," a major city in China.
Here, '上海' denotes Shanghai as a context for its population attribute.
上海は中国で最も人口の多い都市の一つです。
Shanghai is one of the most populous cities in China.
In this sentence, '上海' refers to the city Shanghai as a geographical location.
私は去年、上海を訪れました。
I visited Shanghai last year.
This usage of '上海' indicates the city as a cultural and historical focal point.