Here's a breakdown:

* Exergonic reactions release energy (have a negative ΔG, meaning they are spontaneous).

* Endergonic reactions require energy input (have a positive ΔG, meaning they are non-spontaneous).

Coupling is a mechanism that links these two types of reactions. The energy released from the exergonic reaction is used to power the endergonic reaction. This creates a favorable overall energy change for the coupled reactions.

A classic example is the coupling of ATP hydrolysis (exergonic) to drive the synthesis of proteins (endergonic).

Let me know if you'd like to delve into more detail on this process!