Listing variations are product options shown within the same listing. Or, as Amazon defines it:
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.
More specifically, they’re products listed on the same product detail page that differ in only one (or two) ways.
For example, rather than having five separate listings for a pillow that comes in five different colors, you can group them together on the same detail page, with the five different ASIN variations shown as color choices.
Even though the ASINs will share a detail page, you still need to enter product information for each child ASIN, with a corresponding photo. You’ll notice that when a child ASIN is selected, the product info shown will be for that specific ASIN.
In search results, only one product from the variation group will show. Which product that is depends on the category. In Clothing, Accessories & Luggage, Sporting Goods, and Beauty categories, the parent ASIN shows in search results. In other categories, the bestselling child ASIN shows in search results.