In A/B testing or split testing, a control is a page of a website or version of an app screen you use as reference and compare against other variants, with the purpose of finding those areas that can be improved for increasing conversions or other metrics. The changes on the variants can be minimal compared to the control page, but you can also test two pages that look completely different. At the end of a test, the control page should be replaced with the tested variant only if you obtained statistically significant improvements of the relevant metrics.