Title: Fancy Dress Festival
Content:  The name "Fancy Dress" was used because the Egyaa group, which was made up of fishermen who spoke no English, had a hard time pronouncing the word "masquerade". Instead, they used the term "Fancy Dress", which they pronounced "fanti dress".
Title: Costume party
Content:   The origins of fancy dress parties in the United Kingdom can in some respects be traced to masked balls of the 18th century period. In the period to 1850, fancy dress balls were a typical part of the social life of music festivals. Common costumes of the period were specific historical characters, generic historical or regional clothing, abstract concepts (such as "winter", "starlight" or "night"), and objects (such as "champagne bottle" or "aquarium"). Popular characters included, for women, Marie Antoinette and Elizabeth I, and for men, Napoleon and Robin Hood.
Title: Fancy dance
Content:  headband, and other feathered or beaded accouterments. The regalia often has a fringe of many colors. The old style regalia is making a comeback. The women's fancy shawl dance represents the opening of a cocoon when the butterfly emerges. The shawl is usually the most extravagant piece. The fringed shawls are colorful and flashy, often featuring embroidery or ribbon work. The fringe on the shawl have a movement that coincides with the dancer. The dancers usually wear beaded or appliqued designs, and beaded hairpieces. Chokers, earrings, bracelets, and eagle plumes are usually worn as well. Elaborate moccasins and leggings complete the regalia. The practice of women's fancy shawl dance is far more recent than that of Men's Fancy Dance. It wasn't until fancy dance had existed for several decades that women began to participate.
Title: Costume party
Content:  Australian fancy dress parties typically follow the style of the United States, and Halloween costume parties have been common since the early 1990s, even though Halloween has not historically been a celebrated event in Australia. Typical events for Australians that involve dressing up are the Sydney Gay and Lesbian Mardi Gras, the staff Christmas party and cricket matches. One of the oldest examples of fancy dress being worn in Australia is on display at the Western Australia Museum. It was a child's fancy dress costume worn by Rita Lloyd, aged nine, to the ‘Lord Mayor’s Juvenile Fancy Dress Ball’ at Mansion House in Perth on 8 January 1909.
Title: Costume party
Content:   A costume party (American English) or a fancy dress party (British English) is a type of party, common mainly in contemporary Western culture, where many of the guests are dressed up in costumes. Costumed Halloween parties are popular in the United States, Canada, Australia, and New Zealand.
Title: Frock
Content:  In contemporary times, a "frock" may still designate a woman's or girl's, or child's dress or light overdress.
Title: Dress
Content:  A dress (also known as a frock or a gown) is a garment traditionally worn by women or girls consisting of a skirt with an attached bodice (or a matching bodice giving the effect of a one-piece garment). It consists of a top piece that covers the torso and hangs down over the legs. A dress can be any one-piece garment containing a skirt of any length, and can be formal or casual. A dress can have sleeves, straps, or be held up with elastic around the chest, leaving the shoulders bare. Dresses also vary in color. The hemlines of dresses vary depending on modesty, weather, fashion or the personal taste of the wearer.
Title: Court uniform and dress in the United Kingdom
Content:  feathers (usually three in number) were to be worn (to be 'mounted as a Prince of Wales plume', according to the instructions given in Dress worn at Court) - a style which had its origin in fashionable eighteenth-century daywear. In addition, a short veil was worn, and/or lace lappets (first seen in the 1660s, and still being worn by some ladies in the 1930s). By the end of the nineteenth century, the main occasions at which court dresses were worn were those at which debutantes were presented to the Queen. In the twentieth century (especially following the First World War), occasions for full court dress diminished. It was still required 
Title: Court uniform and dress in the United Kingdom
Content:  For women (as for men) court dress originally meant the best and most opulent style of clothing, as worn in fashionable and royal society. A distinctive style can be seen in the dresses and accoutrements worn by courtly ladies in the Elizabethan period, and likewise in subsequent reigns. The Commonwealth put a stop to Court activity – and to opulent display in general; but with the Restoration, the opportunities afforded by attendance at the royal court was taken up all the more zealously by young women of status or aspiration (and their families). Fashion (and wealth) continued to dictate what was worn on these occasions; but in the late eighteenth century, 
Title: Costume party
Content:  parties are popular year round in the United Kingdom. The 1996 novel Bridget Jones's Diary features the classic British costume party theme "Tarts and Vicars" at which the women wear sexually provocative ("tart") costumes, while the men dress as Anglican priests ("vicars"). Fancy dress parties have been held by the British Royal Family. Prince William, heir to the British Throne, celebrated his 21st birthday with an "Out of Africa" theme, Princess Beatrice of York chose an 1888 themed party for her 18th birthday, and Lord Frederick ("Freddie") Windsor and his sister Lady Gabriella Windsor, celebrated a joint birthday party with a pre-French Revolution courtly theme.

Question: what does fancy dress mean in the uk?
Answer: A costume.
guests dress up in costumes.
costumes.