Concrete is a substance used for building which is made by mixing together cement, sand, small stones, and water.

When you concrete something such as a path, you cover it with concrete.

You use concrete to indicate that something is definite and specific.

A concrete object is a real, physical object.

A concrete noun is a noun that refers to a physical object rather than to a quality or idea.

If a plan or idea is set in concrete or embedded in concrete, it is fixed and cannot be changed.