Usually, A/B Testing experiments will test variations of a certain page or post. However, it's also possible to test other elements (such as themes, CSS code, or titles).
If we focus on the first type of experiments, the original page (or post) is the WordPress page or post from your site that you want to improve. To do so, you create alternative versions of that page so that you end up with one or more alternative version to put under test.
See also more information about how to create a new experiment in our Getting Started Guide.