Most commonly it’s “the viva” but I’ve also heard people refer to it – the event, the exam – as thesis examination, thesis defence, defending your thesis and of course the full viva voce.
I’ve also heard people call the viva, for various reasons: the interrogation, the End, the final hurdle and “I can’t even say it, I’m just dreading it!”
All of these people are talking about the same thing, but all from different personal perspectives. Whatever label they attach, whatever word they use, influences and reinforces how they think about it.
If you label your viva as “my interrogation” then I can imagine you won’t be looking forward to it. “Thesis examination” is quite neutral, neither hot nor cold. If it’s “the End” it’s possible you’re not being negative about it, but maybe you are. The label – the name – you give to your viva, influences how you think about it…
…but you can change the name. It’s a choice. So if you feel negative about it now, perhaps finding out more about the viva can change that feeling. Getting better expectations – both of the event and how you could be prepared – can help you to find a better name for it.
It’s OK if you just name it “the viva.” It’s fine if you call it something else. But the name always means something.
I suppose what I’m trying to say is: pick the most helpful name that you can.