At the start of your PhD you have gaps: the things your research seeks to address.
At the end of your PhD you have holes: the things you didn’t get to, couldn’t show or don’t know.
Both need some of your viva preparation time. Reflect on the research gap to better share it with your examiners. Explore the holes so you can talk about them confidently in the viva.
Your thesis and research are more than gaps and holes, of course, but both will matter in the viva.