What is the botanical classification for the kernel of grains such as wheat and rice?

A caryopsis, which is a type of dry fruit where the seed coat is fused to the ovary wall.

Grains like wheat, rice, and corn are derived from grasses, and their edible component, the kernel, has a precise botanical classification. The kernel is defined as a caryopsis, which is a specific type of dry fruit. The defining characteristic of a caryopsis is that the protective layer of the seed coat is completely fused together with the wall of the ovary (the fruit wall). Therefore, when consuming these grains, you are consuming a fruit structure where the seed is inseparable from its casing. Corn on the cob demonstrates this clearly when the kernels, which are the seeds, are eaten while still moist. This contrasts with legumes (beans, peas), which are seeds that develop inside a distinct pod, which itself is a fruit.