A/B or AB testing refers to testing two different versions of a page or a page element such as a heading, image or button.
The alternatives are served alternately with the visitors to the page randomly split between the two pages. Hence, it is sometimes called live split testing. Changes in visitor behaviour can then be compared using different metrics such as click-through rate on page elements like buttons or images, or macro-conversion rates, such as conversion to sale or sign-up.
AB testing is aimed at increasing page or site effectiveness against key performance indicators including click-through rate, conversion rates and revenue per visit. Since it does not consider combinations of variables tested, for best uplift multivariate testing is increasingly used.