What do you understand is the most important characteristic of a work of art?

This sounds like a personal reflection on something you did. it is asking the hardest part, or a part you may have struggled with on an informal interview you must have done. it is also asking advice you'd give someone else for the process of completing an informal interview, so you should write something that would . for example, maybe the first thing they should do, something they should include.

When an orchestra plays at a concert they might play a symphony (a piece for orchestra) and they might play a concerto (with a soloist). if the solo instrument is a violin the piece is called a “violin concerto”, if it is a piano it is called a “piano concerto”, etc.