Evil-favoredness describes a blemish, defect, lack of symmetry, or lean condition. It could make an otherwise clean animal unfit for sacrifice and could also describe poorly formed or lean cattle.
The Law excludes an animal with such a defect from sacrificial use. Pharaoh’s dream likewise includes seven ill-favored and lean-fleshed cows.
The expression literally means “evil thing” and refers to an animal’s ritual unfitness because of physical defect or lack of acceptable form.