Okay kiddo, so British diaspora refers to all the people who come from the United Kingdom but now live in different parts of the world like America, Canada, Australia, and other countries.
You know how when grandma comes to visit us, she's from another place but now lives here with us? It's kind of like that, but with many more people and in lots of different countries.
Some people moved to other countries a long time ago, like when America was just starting and people from Britain moved there for a new life. Other people moved more recently, maybe for work or because they wanted to live somewhere different.
Even though these people live in different places now, they still might feel connected to their British roots and celebrate British holidays or traditions. They might also learn about their family history and where their ancestors came from in the UK.
Does that make sense, little one?