Here's why:
* Abstract nouns represent ideas, concepts, qualities, or states of being. They are not physical things you can touch.
* Discussion is a process of exchanging ideas and opinions. It's not a tangible thing.
Let's compare it to a concrete noun:
* Table is a concrete noun because it's a physical object you can touch.
Therefore, "discussion" is an abstract noun because it refers to a concept, not a physical thing.