The Latin term viva voce means "the living voice". The oral examination of a thesis for a doctoral degree is thus seen to be a more 'living' assessment opportunity whereby the candidate can have a conversation with examiners, rebut arguments, clarify any confusions and ambiguities, take advice for improvements of the thesis, and get developmental feedback for future research endeavours. The event is variously referred to as a 'viva', 'oral defence', 'thesis defence', or 'oral examination', with the wording possibly implying differences in purpose (Murray, 2002). 

Access and download the publication: BrieflySpeaking No. 30 - Viva Voce: The Oral Examination of a Thesis for a Doctoral Degree