A/B testing (also called split testing) is comparing multiple versions of a web page to see which one performs better. You compare two web pages by showing two variations (let's call them A and B) to your visitors at the same time. Showing them to similar visitors and at the same time is very important. That's where nagg comes in. You present one link to your visitors and we take care of splitting them into multiple URL's.
See below for an example of a test commonly used.