Examples are: flower, bird, book, sand, star, butterfly, cloud etc.
Nouns can be classified into several categories such as , abstract and concrete nouns, , etc.
If you can sense a noun by your five senses and it is referring to a specific concept then you have to write it with a capital letter in the beginning and it is called a proper concrete noun, however, if it is referring to a generic concept then it is considered a common concrete noun and it is not capitalized in the beginning.
The two of them can be categorized differently on a different basis.
.
GrammarEdge is an initiative to make English easy to learn and understand.