Someone or something has "IT" when they have some amazing special quality. Mostly cannot be narrowly defined. Spoken, emphasis is put on the word "it".
She tries really hard to be a model, but she doesn't have IT.
Beyoncé is more than just a singer and actress, she has IT.
You should get that wedding gown. It just has IT.
Man, that guy has everything. He has IT.
November 1st of every year we celebrate Leave Your Parents Alone Day. The kids have a ton of candy, TV and video games. They do not need a nutritious dinner for once. Parents are allowed to do anything they want to, including participating in eating candy, watching TV and playing video games. Kids are not allowed to fight, or everything gets taken away from all of the kids (even the innocent ones), and they are sent into solitary confinement for the remainder of the day.
November 1st is Leave Your Parents Alone Day