Is a coupled rxn any rxn that combines 1 endergonic and 1 exergonic rxns? So then in glycolysis, step 6, GA3P ---> 1,3diPGA plus NAD--->NADH2; and before the Krebs cycle, pyr ---> acetyl-CoA plus NAD reduction; and in the Krebs cycle, isocitric acid ---> keto plus NAD reduction... Are all these three rxns examples of coupling?
In the broadest sense, we can talk about two reactions coupled to contrast the same two reactions not coupled, that is, occuring independently. This is easy to see for the first such coupled reaction we considered, the phosphorylation of glucose by ATP instead by phosphate addition. For the cases you cite, it is a little more difficult to see the reactions independently, since they are oxidation-reductions and so are obligatorily coupled. Nevertheless, in English terms, we can talk abstractly about the reduction of NAD to NADH2, and the oxidation of pyruvate to acetyl-CoA and CO2, as separate "paper" reactions, that are then coupled in the actual reaction leading to the Krebs cycle.