Basic Trope: Something's revealed to the characters, but the viewer is still left in the dark.
Straight: The Master reveals his true name to Alice. "My true name is... * whisper whisper* "
Exaggerated: Alice has bad hearing and asks the Master to repeat his name several times. He whispers every time.
The viewers are not given the Master's name, but they are given a few subtle clues that they can use to figure out his name.
Alice responds by saying "It doesn't matter what your name is."
Justified: The Master is very careful about who he reveals his true name to, because it could be used as power against him. The fact that we're as able to hear it only as well as potential witnesses are is just coincidence.
Only the name is heard, but everything else is in whispers so we have no idea who the name belongs to.
The characters leave... And the camera pans to show the viewer the answer.
Invoked: "No one else can hear this...* whisper whisper* "
Defied: "Now, and I am going to make sure you all hear this..."
Discussed: "Aw, we didn't hear him. This must be one of those deals where the author intentionally leaves the viewer in the dark."
Conversed: "...And if I know the director, the Master's name will be in whispers and we won't hear a bit of it."
Deconstructed: When the master refuses to disclose his name to his students after twenty years, his students feel they can no longer trust him. They leave him, stating that they can't trust someone unwilling to give them their most basic information. Without students, he can no longer teach.
Reconstructed: Before dying of sickness, he tracks down his student, saying he wants to tell him his name. He dies seconds before he can say it aloud.