In 2009, the people of Denmark were asked to vote on a decision about who would be allowed to become their new king or queen. In Denmark, it used to be that only men could become the king, but people wanted to change that rule so that women could also become queen.
The vote was called the "Danish Act of Succession Referendum," which means that it was a big decision for the Danish people about who would be the new leader of their country. The vote was important because it would change the rules about who could become king or queen in the future.
The vote was very simple. People were asked to vote "yes" or "no" on whether they wanted to change the rules so that women could become queen. If more than half of the people that voted said "yes," the rule would be changed and women would be allowed to become queen.
In the end, the people of Denmark overwhelmingly voted "yes" to change the rule. This meant that if the current king, who was a man, did not have any sons, his oldest daughter could become the new queen one day.
Overall, the Danish Act of Succession Referendum was an important decision for the people of Denmark, as they were able to vote on a significant change in their country's leadership rules.