Nails are similar to claws, which are found on numerous other animals. In common usage, the word nail often refers to the nail plate only.
The nail consists of the nail plate, the nail matrix and the nail bed below it, and the grooves surrounding it.
In mammals, the length and growth rate of nails is related to the length of the terminal phalanges (outermost finger bones). Thus, in humans, the nail of the index finger grow faster than that of the little finger; and fingernails grow up to four times faster than toenails.
In humans, nails grow at an average rate of 3 mm (0.12 in) a month (as they are a form of hair). Fingernails require 3 to 6 months to regrow completely, and toenails require 12 to 18 months. Actual growth rate is dependent upon age, gender, season, exercise level, diet, and hereditary factors. Nails grow faster in the summer than in any other season. Contrary to popular belief, nails do not continue to grow after death; the skin dehydrates and tightens, making the nails (and hair) appear to grow.