What is NADH in glycolysis?

In glycolysis, NADH is generated during the oxidation of glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate. NAD+ acts as an electron carrier, accepting electrons from G3P, and becomes reduced to NADH. NADH carries these high-energy electrons to the electron transport chain in aerobic conditions or to fermentation pathways in anaerobic conditions, where NAD+ is regenerated for continued glycolysis.