The 'it' girl; refers to a girl or a woman that has 'it' which is intelligence,charm ,beauty, personality, sex appeal and success. This expression came about in the 1920's I believe.

It girl= the most popular actress or model at this time

It means, a desirable girl. She has "it", which is charm, sexiness, etc. The first "it girl" was Clara Bow. Example: "Looks like [such-and-such an actress] is going to be the new it-girl."

I don't know

全句是？