This is the 2375th most frequent Chinese word.
北平
"北平" means "Beiping," the former name of Beijing used historically, especially before 1949.
Here, 北平 refers to the city during a historical period when its name was different from today, making it a proper noun.
北平是中国历史上的一个著名城市。
Beiping is a famous city in Chinese history.
北平 is used here as the historical name for present-day Beijing, explaining its historical context.
在那个年代，人们都称现在的北京市为北平。
During that era, people referred to today's Beijing as Beiping.
The sentence uses 北平 as a focal point to discuss cultural aspects related to its historical identity.