A noun is a word that names a person, a place, a thing, or an idea.
A concrete noun is a person, a place, or a thing that we can see.
When the concrete noun is common, it is not specific and it does not get capitalized.
Here are some concrete common nouns that name a person:
teacher
mother
father
sister
brother
doctor
mechanic
Here are some concrete common nouns that name a place:
school
home
garage
playground
grocery store
gym
bedroom
Here are some concrete common nouns that name a thing:
basketball
sandwich
dog
tree
bicycle
stone
book
We use concrete common nouns to name objects in the world that can be seen. Concrete common nouns name persons, places, and things.