Child ASIN
Each product on Amazon receives a Child ASIN, making the product uniquely identifyable for Amazon's catalogue.
Parent ASIN
If a product consists of multiple similar variations (eg. the same dress in white, as well as black), these variations can be grouped within a Parent. The Parent ASIN therefore does not represent an actual product, but merely summarizes a group of variations.
All products within a parent share the same reviews.