The words “concrete” and “particular” get commonly confused by English learners. Of course, we are not talking about “concrete” in the sense of “made of concrete” (the building material), as in “a concrete wall”. We are talking about “concrete” as in “a concrete example”.
Statistically speaking, if you are reading this, the word you are probably looking for is “particular”, which is about 10x as common as “concrete” in English. It is used to emphasize that you are talking about just a single individual or thing, e.g.
“Concrete”, being much less common than “particular”, is most commonly used in the sense of “tangible, real” when talking about evidence and proofs:
or in the sense of “not abstract, specific” when talking about examples: