An "it girl" is an attractive young woman, generally a celebrity, who is perceived to have both sex appeal and a personality that is especially engaging.
The expression it girl originated in British upper-class society around the turn of the 20th century. It gained further attention in 1927 with the popularity of the Paramount Studios film "It", starring Clara Bow. In the earlier usage, a woman was especially perceived as an it girl if she had achieved a high level of popularity without flaunting her sexuality. Today, the term is used more to apply simply to fame and beauty. The Oxford English Dictionary distinguishes between the chiefly American usage of "a glamorous, vivacious, or sexually attractive actress, model, etc.", and the chiefly British usage of "a young, rich woman who has achieved celebrity because of her socialite lifestyle".
The male version of an "it girl" is an "it boy".
An early literary usage of it in this sense is found in to a 1904 short story by Rudyard Kipling, which contains the line "'Tisn't beauty, so to speak, nor good talk necessarily. It's just It. Some women'll stay in a man's memory if they once walk down a street."
Elinor Glyn, the notorious British novelist who wrote the book titled It and its subsequent screenplay, lectured:
With It, you win all men if you are a woman and all women if you are a man. It can be a quality of the mind as well as a physical attraction.— Elinor Glyn (1927)
Glyn first rose to fame as the author of the scandalous 1907 bestseller Three Weeks. She is widely credited with the invention of the "It Girl" concept: although the slang predates her book and film, she was responsible for the term's impact on the culture of the 1920s.
Clara Bow later said she wasn't sure what "It" meant, although she identified Lana Turner and later Marilyn Monroe as "It Girls", and Robert Mitchum as an "It Man".
The fashion component of the It Girl originated with the celebrated couturier Lucy, Lady Duff-Gordon, known professionally as "Lucile", the name under which she managed exclusive salons in London, Paris and New York; she was Elinor Glyn's elder sister. As Lucile, Lucy Duff-Gordon was the first designer to present her collections on a stage complete with the theatrical accoutrements of lights and music, inspiring the modern runway or catwalk show, and she was famous for making sexuality an aspect of fashion through her provocative lingerie and lingerie-inspired clothes. Lucile also specialised in dressing trendsetting stage and film performers, ranging from the stars of the Ziegfeld Follies on Broadway to silent screen icons such as Mary Pickford and Irene Castle.
As early as 1917, Lucile herself used the term It in relation to style in her fashion column for Harper's Bazaar: "... I saw a very ladylike and well-bred friend of mine in her newest Parisian frock ... she felt she was 'it' and perfectly happy."
The Paramount Studios film was planned as a special showcase for its popular star Clara Bow, and her spectacular performance introduced the term "It" to the cultural lexicon. The film plays with the notion that "It" is a quality which eschews definitions and categories; consequently, the girl portrayed by Bow is an amalgam of an ingenue and a femme fatale, with a touch of Madonna's latter day "Material Girl" incarnation. By contrast, Bow's rival in the script is equally young and comely (and rich and well-bred to boot), yet she doesn't have "It".
Since the 1980s, It Girl or It-Girl has been used slightly differently, referring to a wealthy, normally unemployed, young woman who is pictured in tabloids going to many parties often in the company of other celebrities, receiving media coverage in spite of no real personal achievements or TV hosting / presenting. The writer William Donaldson observed that, having initially been coined in the 1920s, the term was applied in the 1990s to describe "a young woman of noticeable 'sex appeal' who occupied herself by shoe shopping and party-going".
The prominence of an "It Girl" is often temporary; some of the rising It Girls will either become fully-fledged celebrities, commonly initially via engineering appearances on reality TV shows or series; lacking such an accelerant, their popularity will normally fade.
... she had that indefinable quality which Kipling was the first to call 'It' – sex-appeal without flaunting her sexuality.