Data fusion is when you combine data from multiple sources to create a larger set of data. Imagine if you wanted to know how to best sell a particular product. You could look at the sales from different stores that sell that product, but that would still leave you with a lot of unanswered questions, like how much different stores were selling it for, what were customers saying about it, how old were customers buying it, etc. With data fusion, you can combine the sales data with customer reviews, age group information, price information, and more to get a fuller picture of how the product is selling. This makes it easier to make better decisions about selling the product.