waht the mean is concrete approach?

I found this term in chess books several times, but the truth was I did not find an explanation for it.

Do I understand that it is a strong and complex postition or is it not?

Playing with heavy concrete chess sets(?)... 

Concrete play means moves are justified via calculation (which is only possible when there are threats).

The opposite would be something positional like "I played Rd1 because it's on an open file" or "I played Ng5 because I want to attack, so I'm moving pieces near Black's king"

Concrete would be "I played Rd1 because the threat is Rxd8 so my opponent is forced to play ___ and then I'll play ____ (etc, a list of moves). 

Or "I played Ng5 because the threat is Rxh7 and so my opponent is forced to play option A or B and then..." (etc)

If it's an instructional book, I'd say it's a useful annotation to let the reader know not to draw any rules of thumb from the following sequence. There's nothing you can generalize. The moves are good but only because of the specifics of the unique position... I suppose that's another way of saying it.

It may also be useful to note because when a GM is playing "concretely" it may not be obvious  to the reader that there are threats or that the opponent's responses are very limited.

So... same as my post said?

Ok