AB testing, also known as split testing or bucket testing, involves testing two versions of a webpage element (A and B) and measuring a specific metric to determine which performs better. The document discusses how AB testing works by randomly distributing visitors to different page versions and measuring metrics like bounce rate and click-through rate. It also outlines the typical AB testing process of measuring performance, testing variations, evaluating results, and optimizing the best performing version. Benefits include measuring real user behavior, determining what drives conversions, and ability to test small differences with large traffic. Limitations include needing clearly defined goals and fully implemented designs to test.