A walnut is the edible seed of any tree of the genus Juglans, particularly the Persian or English walnut, Juglans regia. They are accessory fruit because the outer covering of the fruit is technically an involucre and thus not morphologically part of the carpel; this means it cannot be a drupe but is instead a drupe-like nut.
Walnut kernel, halves
Walnuts
Inside of a walnut in growth
Three-segment walnut
In botany, a seed is a plant embryo and food reserve enclosed in a protective outer covering called a seed coat (testa). More generally, the term "seed" means anything that can be sown, which may include seed and husk or tuber. Seeds are the product of the ripened ovule, after the embryo sac is fertilized by sperm from pollen, forming a zygote. The embryo within a seed develops from the zygote and grows within the mother plant to a certain size before growth is halted.
Photomicrograph of various seeds
The inside of a Ginkgo seed, showing a well-developed embryo, nutritive tissue (megagametophyte), and a bit of the surrounding seed coat
Seed coat of pomegranate
A collection of various vegetable and herb seeds