A fingerprint is an impression left by the friction ridges of a human finger. A friction ridge is a raised portion of the epidermis on the fingers and toes, the palm of the hand or the sole of the foot, consisting of one or more connected ridge units of friction ridge skin. These are sometimes known as epidermal ridges which are caused by the underlying interface between the dermal papillae of the dermis and the interpapillary pegs of the epidermis. These epidermal ridges serve to amplify vibrations triggered, for example, when fingertips brush across an uneven surface, better transmitting the signals to sensory nerves involved in fine texture perception. These ridges also assist in gripping rough surfaces, as well as smooth wet surfaces.
Impressions of fingerprints may be left behind on a surface by the natural secretions of sweat from the eccrine glands that are present in friction ridge skin, or they may be made by ink or other substances transferred from the peaks of friction ridges on the skin to a relatively smooth surface. Fingerprint records normally contain impressions from the pad on the last joint of fingers and thumbs.
Adapted from the fingerprint entry on Wiki.
I’m not sure why I like this description so much, but it sort of reads like poetry to me. I’m going to do something with this in a story or something. Oops, I’ve just reavealed a secret.