Online Arbitrage (OA) is the process of buying products at a lower price from online retailers and selling them on Amazon for a higher price. It differs from wholesale, where sellers buy items in bulk from manufacturers or distributors, and private label, where sellers create their own brand and product line. OA focuses on leveraging price discrepancies across different online platforms to earn profits, while wholesale and private label concentrate on building a consistent brand and long-term relationships with suppliers.