A hat is a head covering. It can be worn for protection against the elements, for ceremonial or religious reasons, for safety, or as a fashion accessory. In the past, hats were an indicator of social status. In the military, they may denote nationality, branch of service, rank and/or regiment
One of the first pictorial depictions of a hat appears in a Thebes tomb painting which shows a man wearing a coolie-style straw hat. Other early hats were the Pileus, a simple skull cap; the Phrygian cap, worn by freed slaves in Greece and Rome; and the Greek petasos, the first known hat with a brim. Women wore veils, kerchiefs, hoods, caps and wimples. St. Clement, the patron saint of felt hatmakers, is said to have discovered wool felt when he filled his sandals with flax fibers to protect his feet. Structured hats for women similar to those of male courtiers began to be worn in the late 16th century. The term ‘milliner’ comes from the Italian city of Milan, where the best quality hats were made in the 18th century. Millinery was traditionally a woman’s occupation, with the milliner not only creating hats and bonnets but also choosing lace, trimmings and accessories to complete an outfit.
In the first half of the 19th century, women wore bonnets that gradually became larger, decorated with ribbons, flowers, feathers and gauze trims. By the end of the century, many other styles were introduced, among them hats with wide brims and flat crowns, the flower pot and the toque. By the middle of the 1920s, when women began to cut their hair short, they chose hats that hugged the head like a helmet.
Since the early 21st century, flamboyant hats have made a comeback, with a new wave of competitive young milliners designing creations that include turban caps, tromp l'oeil effect felt hats and tall headpieces made of human hair. Some new hat collections have been described as "wearable sculpture." Many pop stars, among them Lady Gaga, have commissioned hats as publicity stunts.
read more at http://en.wikipedia.org/wiki/Hat
