* Abstract nouns represent concepts, ideas, qualities, or feelings that cannot be physically touched or seen. Harmony represents a state of agreement, balance, and concord. You can't hold harmony in your hand or see it with your eyes.
* Concrete nouns, on the other hand, refer to things that are tangible and have physical existence. For example, "table" or "tree" are concrete nouns.
Since harmony is an intangible concept, it falls under the category of abstract nouns.