Final answer:
The term for the half-moon structure on the nail is the lunula, a visible part of the nail matrix appearing as a whitish crescent shape at the base of the nail, involved in the nail growth process.
Step-by-step explanation:
The term that describes the half-moon structure found in the nail is the lunula.
The lunula is the visible part of the nail matrix and appears as a whitish crescent at the base of the nail. Structurally, it is a thick layer of epithelium over the nail matrix.
The lunula is most prominent on the thumb and can be seen through the nail body as it forms at the nail root, which has a matrix of proliferating cells from the stratum basale.
The function and continuous growth of the nail are thanks to this matrix. Alongside the lunula, the nail bed is a key component of the nail structure; it's rich in blood vessels, giving the nail its pink color, except at the lunula.
The nail body (or plate), which is the hard part of the nail, is formed on the nail bed and consists of densely packed dead keratinocytes.