Baby marrow is the British, South African, and Commonwealth term for a small, immature zucchini or courgette, harvested at 4-8 inches long before the skin toughens and the seeds develop. The squash species it comes from was domesticated in the Americas thousands of years ago, but the specific slender green cultivar known as zucchini was bred in Italy in the 19th century. Its thin skin is edible and needs little prep; it's commonly sautéed, grilled, roasted, steamed, or stuffed, and its mild flavor works with herbs, garlic, cheese, and other summer vegetables. It's also spiralized or grated raw as a low-carb pasta substitute.