Okay kiddo, so you know how every country has people who work for the government to help make important decisions, right? Well, in the United Kingdom a long time ago there was a person who had a really fancy job called the Secretary of State for Dominion Affairs.
Now, a "dominion" is another word for a "colony" or a place that is ruled by another country. Back in the old days, the UK owned a lot of colonies all over the world, and it was the job of the Secretary of State for Dominion Affairs to help look after them and make sure everything was running smoothly.
This person was kind of like a big boss for all the different countries that were a part of the British Empire. They talked to the leaders of those countries and helped make important decisions about things like trade and security.
But even though this job was very important, it doesn't really exist anymore. The British Empire isn't as big as it used to be, and now the UK has other people in charge of looking after different countries. So while the Secretary of State for Dominion Affairs was a big deal a long time ago, nowadays it's just something we learn about in history books!