A/B test, also known as split testing, is a method of comparing two versions of a webpage, email, or advertisement to determine which one performs better. This is done by randomly dividing the audience into two groups and showing each group a different version. The results of the test are then analyzed to determine which version is more effective in achieving the desired outcome, such as higher click-through rates or conversions. A/B testing is commonly used in marketing and website optimization to make data-driven decisions and improve overall performance.