Fascinators: The Hat of Choice at the Royal Wedding...

David and Victoria Beckham (wearing a floral Philip Treacy Fascinator) attend the wedding of William & Kate

A fascinator is a headpiece, a style of millinery. The word originally referred to a fine, lacy head covering akin to a shawl and made from wool or lace. The term had fallen almost into disuse by the 1970s.
In the early 21st century, the term has made a comeback, but the meaning has slightly changed; it is now used to describe a delicate, slightly-to-very frivolous head decoration worn almost exclusively by women. A fascinator may be worn instead of a hat to occasions where hats were traditionally worn—such as weddings—or as an evening accessory, when it may be called a cocktail hat. It is generally worn with fairly formal attire.
See Royal Wedding Hats and Fascinators
A substantial fascinator is a fascinator of some size or bulk. They have been mentioned in the press, due to Queen Elizabeth pronouncing new standards of dress required for entry to Royal Ascot.
Modern fascinators are commonly made with feathers, flowers or beads. They attach to the hair by a comb, headband or clip. They are particularly popular at premium horse-racing events, such as the Grand National and the Melbourne Cup. Brides may choose to wear them as an alternative to a bridal veil or hat, particularly if their gowns are non-traditional.