In your viva you might be able to handwave some details.
To have time to explore the truly important aspects of your work you might want to skip past tricky things, or make a short point that captures something big. That’s acceptable to do. You can say, effectively, “Trust me. This is the way it is and we don’t need to explore or explain it too much.”
It’s acceptable, but it’s also acceptable for your examiners to say, “Prove it.”
You can use whatever words you want in the viva to explain something. Your examiners can always ask for more detail. While you can say things as simply as you want, you have to be prepared to explore the complex.
