Quick answer
An eco-friendly or 'green' house wire is made with safer, more sustainable materials — typically lead-free, RoHS-compliant insulation that is also low-smoke and halogen-free. In a fire it releases far less toxic gas, and over its life it avoids the hazardous additives of ordinary PVC.
Green wiring also tends to last longer and run more efficiently (less energy lost as heat), so you replace less and waste less. APAR's Green Wire (HR-FR-LSH PVC) is built around exactly this — eco-friendly, lead-free, fire-safe.