Overview
As a food
Oyakodon (親子丼) is a type of Asian cuisine originating from Japan. Part of the donburi dish, the oyakodon consists of ingredients simmered together in soy sauce with chicken, egg, onions and other ingredients, then topped off in a bowl of rice altogether.
Oyakodon can literally translate as "parent-and-child donburi."
As a euphemism
In Japan, the word 'oyakodon' could be used to describe where a person has their way with a parent-and-child. In other words: a threesome. Taking the literal translation from above, the word in this context may refer to any parent or child, be it father-and-son, or mother-and-daughter. In a more serious case, the context always applies to mother-and-daughter.
Overall
So far, this tag on Pixiv is often used for R-18 works denoting sexual encounters with a mother and daughter. There are not quite a lot of food-only artwork consisting of the oyakodon dish in this category and filtering for food-specific artwork is difficult due to the usage of this term/tag on the site.
Related Articles
Food
Relationship
bowl of sisters kinshin soukan