"What is a concrete noun?" you ask.

"It's something you can drop on your foot. It's that simple."

"So if I am writing about markets, productivity and wealth, I am going to...."

"Yes indeed -- you are going to write about things you can drop on your foot, and people, too. Green peppers, ears of corn, windshield wipers, or a grimy mechanic changing your car's oil. No matter how abstract your topic, how intangible, your first step is to find things you can drop on your foot."

from https://www.theatlantic.com/national/archive/2012/10/the-secret-to-good-writing-its-about-objects-not-ideas/263113/