A/B Testing (or split testing) is an optimization method where two versions of an element (page, ad, email) are shown simultaneously to different user groups. The version that drives more conversions or better engagement wins and gets implemented permanently.
An online store tests two CTA button variants: 'Buy Now' vs 'Add to Cart'. After 2 weeks and 5,000 visitors per variant, 'Add to Cart' generates 23% more conversions.