A/B/n testing is a process where you expose a percentage of visitors to different versions of your website. It differs from A/B, however; in that AB will have at least three variations on display at any given time in your site.
In addition to the control, you would also have at least three additional variations of your website being tested—perhaps a different landing page graphic for example. Your website visits will be evenly distributed between the 4 pages based on their number of views.
When designing a conversion funnel, you want to start by testing variations on your homepage. At the end of that test, you can see which variation had the best conversion rate and become more confident in moving forward with your marketing campaign.