Chickens and pigs is a metaphor for who's got skin in the game. Or to leave metaphors behind, who's involved in a project vs who is fully committed.
Also known as the bacon and eggs principle, it's from the old joke (sometimes told as a short story), "In a bacon and eggs breakfast, the chicken is involved, but the pig is committed."
Many people may be interested in and share their opinions on a project or decision. But only some will be responsible for delivering the project and directly accountable for its success.
Everyone may be interested in a bet, but only some players have money to lose.
The chickens and pigs metaphor used to be part of the scrum guide for developing software but was removed. While it memorably distinguishes accountability in a project, there's a danger that it alienates or diminishes valuable input that might make a project successful.
For a more conventional grouping of stakeholders in a project, see RACI