The ___ is the whitish half-moon shape at the base of the nail.

The term that describes the whitish half-moon shape at the base of the nail is lunula. This structure is visible as a crescent-shaped area located beneath the proximal nail fold and serves as an important feature in nail anatomy. The lunula is the visible part of the matrix, which is the tissue responsible for nail growth. Understanding the lunula's significance can help in recognizing nail health; an absent or discolored lunula could indicate underlying health issues. The other options refer to different aspects of nail anatomy, such as the sidewall, which is the skin on the sides of the nail, the free edge, which is the part of the nail that extends beyond the fingertip, and the root, which is located beneath the cuticle area and is also part of the nail matrix.