Abstract nouns do not point to specific things.

Abstract algebra is a field of mathematics that studies algebraic structures in an abstract way.

He used a syringe to inject the medicine.

He had to pay a fine for a parking violation.

A neutron is part of an atomic nucleus.

The game was stopped due to sudden rain.

This rock contains a lot of neutral feldspar, especially andesine.

Neutron stars are known for their density and strong gravity.

His thesis is filled with a lot of comments.

He commented on the article.