What is respiratory uncoupling?

When something uncouples the proton motive force from ATP synthesis. Proteins such as thermogenin do this by allowing protons to move across the inner mitochondrial membrane without capturing the energy released to synthesize ATP (the protons are not used by ATP synthase, they instead move down an electrochemical gradient and generate heat). Some compounds do this as well (e.g., dinitrophenol, which shuttles protons across the membrane).