* Abstract nouns represent concepts, qualities, or ideas. They are not physical things you can touch.
* "Obvious" represents the quality of being easily understood or seen. It's not a concrete object.
Examples:
* Concrete noun: The book is on the table. (You can touch a book)
* Abstract noun: The obviousness of the answer surprised everyone. (Obviousness is a quality, not a physical thing)
Let me know if you'd like more examples!