HAIRPIN

A 'hair pin' or 'hairpin' is a long device used to hold a person's hair in place.
Hairpins made of metal, ivory, bronze, carved wood, etc. were used in ancient Assyria and Egypt for securing decorated hairstyles. Such hairpins suggest, as graves show, that many were luxury objects among the Egyptians and later Greeks, Etruscans, and Romans.
The hairpin may be needle-like and encrusted with jewels and ornaments. It often may be more utiliarian—designed to be almost invisible after being inserted into the hairstyle.
Hairpins also may be constructed from different lengths of wire that are bent in half with a u-shaped end and a few kinks along the two opposite portions. The finished pin may vary from two to six inches in final length. The length of the wires enables placement in several styles of hairdos to hold the style in place. The kinks enable retaining the pin during normal movements.
The nature of the U-shaped end of this design gave rise to an adjective to describe a particularly tight 180-degree turn in a road, especially in the context of motorsports: a "hairpin turn" — as shown in the accompanying diagram of a racetrack with several sharp turns.
Sections known as hairpins are also found in the slalom discipline of alpine skiing. A hairpin consists of two consecutive vertical or "closed gates" which must be negotiated very quickly. (Three or more consecutive closed gates are known as a flush.)
Patent in 1925 by Kelly Chamandy - http://patents1.ic.gc.ca/details?patent_number=250155

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In biochemistry

In biochemistry

In biochemistry, the term refers to a stem and loop association of nucleotides with a palindromic sequence that causes them to form hydrogen bonds with their complementary nucleotides on the same strand.
There is also a hairpin-like motif in protein structures, called beta hairpin.