Concrete Noun:
* Refers to the physical building: "I went to school this morning." Here, "school" refers to the actual building where classes are held.
* Refers to a specific institution: "I graduated from Harvard Law School." Here, "school" refers to a specific educational institution with a name and location.
Abstract Noun:
* Refers to the concept of education: "School is important for the development of young minds." Here, "school" represents the general idea of learning and education.
* Refers to a system of education: "The school system in this country needs reform." Here, "school" refers to the entire system of education, not a specific building or institution.
In short:
* Concrete "school" refers to a physical place.
* Abstract "school" refers to the idea of learning and education.
The meaning of "school" depends on the context of the sentence.