Here's why:
* Abstract nouns represent concepts, qualities, ideas, or feelings that you can't touch or see. They are not physical things.
* Virtue represents a moral excellence or a good quality, which is a concept and not something tangible.
Let's compare it to a concrete noun:
* Table is a concrete noun because it represents a physical object you can touch and see.
Since you can't touch or see virtue, it fits the definition of an abstract noun.