Here's why:
* Concrete nouns refer to things that can be touched or perceived by the senses. A computer is a physical object that you can see, touch, and interact with.
Let's compare it to other noun types:
* Abstract nouns refer to ideas, qualities, or concepts that cannot be touched. Examples include happiness, love, freedom.
* Collective nouns refer to a group of people, animals, or things. Examples include team, flock, army.
While a "computer network" could be considered a collective noun, the word "computer" itself is a concrete noun.