The term 'Leaf Under a Petal' is a reference to the sepals of a flower. Sepals are the green, leaf-like structures that form the outermost layer of a flower bud and protect the inner petals. They are typically green in color and can be found at the base of the petals. Sepals are an important part of the flower's reproductive system, as they help to attract pollinators and provide support for the petals.