A cappella
From Angelina Jordan Wiki
Wikipedia has information about:
A cappella refers to singing without musical accompaniment. It literally means "in the chapel" in Italian. Other commonly seen forms of the term in English include a capella and acapella.
Angelina has performed a cappella many times, perhaps most famously in her second-round performance of "I'm a Fool to Want You" on Norske Talenter.
Some other performances of this type can be found in this (very incomplete) playlist:
