Okay kiddo, so in 1991 a big thing happened in Bosnia and Herzegovina. The government wanted to count how many people lived there so they did something called a "population census".
Basically, people went around to all the houses and asked everyone who lived there. They also asked things like how old they were, what language they spoke, and what religion they followed. This helped the government understand more about the people who lived in Bosnia and Herzegovina.
It was an important census because it was done right before a big war happened in the country. This war caused a lot of people to move away or sadly lose their lives. So, by doing the census in 1991, the government could look back and understand how many people were living there before the war started.
It's important to know about this census so that we can understand more about the history of Bosnia and Herzegovina and how the country has changed over time.