Variations (also known as parent-child relationships) are sets of products that are related to one another. Good variation relationship listings allow buyers to compare and choose products based on different attributes such as size, color, or other characteristics from the available options on a single product detail page.
There are 3 elements of a parent-child relationship:
The parent product is a non-buyable product used to relate child products. The Amazon catalog uses the parent product to establish relationships between the child products. For example, if two shirts have the same parent then they are related and are considered child products.
The child product is an instance of the parent product. You can have many child products that are all related to one parent product. Each child varies in some way, for example, variation by size or by color.
The variation theme defines how related products differ from each other. For example, in the Clothing, Accessories & Luggage category, child products can differ from each other by size or color.
You can also use hybrid variation themes. For example, the Clothing, Accessories & Luggage category supports variations by both size and color, so you can use "SizeColor" as a variation theme. See the valid values tab in the inventory file for your specific category to see which types of relatiionships it supports.