A/B testing is a technique used in marketing to compare two versions of an advertisement or website design to determine which one performs better in achieving a specific goal. It involves presenting two versions of the same content to a sample group and measuring the effectiveness of each version based on a predetermined metric such as click-through rate or conversion rate. By comparing the results of the two versions, marketers can gain insights into what works better and make data-driven decisions to improve the performance of their ads or website. A/B testing is an effective tool to optimize marketing campaigns and improve user experience, as it allows marketers to experiment with different strategies and identify the most effective ones for their target audience.