The nail is an unguis, meaning a keratin structure at the end of a digit. Other examples of ungues include the claw, hoof, and talon.

In some cases, nutritional deficiencies, particularly deficiencies in iron or B vitamins, can contribute to changes in nail health, including discoloration or spotting. However, it is important to note that red or black spots on nails are not exclusively caused by dietary deficiencies and can have various other causes.

In woodworking and construction, a nail is a small object made of metal (or wood, called a tree nail or "trunnel") which is used as a fastener, as a peg to hang something, or sometimes as a decoration. Generally, nails have a sharp point on one end and a flattened head on the other, but headless nails are available.

The lunula is the distalmost part of the matrix that can be seen. The matrix appears white due to the thickened epidermis in this region and the light-scattering effect of nucleated cells. The epidermis of the nail bed is thinner and more vascular and is therefore clinically pinker.