In Kill Bill, the name of Uma Thurman's character, Beatrix Kiddo, is bleeped out whenever it is spoken. This was done to create an air of mystery around her character. Director Quentin Tarantino has said that he wanted the audience to wonder why her name was being hidden and to make them feel like they were in on a secret.
While we never learn the reason why her name is bleeped out, there are some theories. One possibility is that she changed her name after she left the Deadly Viper Assassination Squad and went into hiding. Her new identity would be a closely guarded secret, hence the need for the censorship.
Another theory is that Kiddo's real name is so dangerous that even speaking it aloud could bring harm to those around her. This would explain why everyone is so careful not to say it aloud (even when they're alone) and why Budd (Michael Madsen) tells Elle Driver (Daryl Hannah) not to say Kiddo's name when they're fighting.
Whatever the reason for the secrecy, it adds an extra layer of intrigue to an already fascinating character. It also makes us want to know more about Beatrix Kiddo and her past, which is exactly what Tarantino wants us to feel.