An n-Matrix that has multiple dimensions can be split into many new n-matrixes by removing one of the dimensions. This is important when taking items from eBay where many dimensions are supported and publishing them to sites like Amazon, where only size and color are supported. For example, an eBay listing for a baseball cap might have variations by team, color and size and the team dimension would need to be removed before it can be published onto Amazon.
You can split an n-Matrix from the ProductDetail page. 'Split n-Matrix' is an item on the n-Matrix submenu. Once you the original n-matrix has been split, the child skus will be members of more than one parent n-matrix. If you click n-Matrix from the child sku it will then give you the option to navigate to either of the parents.