What control is: in testing terms, the initial, original design or copy (webpage, email, ad)—the one you’re already using.
What control is not: a brand new design/copy you just came up with that you want to test against another brand new design/copy.
Why we care about control: To do a great test, you’ll want to measure relative performance against your control. Without a control, you can still test, but you’ll be testing two brand-new pieces of design/copy against each other, and you won’t see the immediate improvement or loss over your original design/copy.
This post is part of an ongoing Clickipedia series, defining all the terms you need to know for conversion rate optimization. Keep checking back each week to learn more, and don’t forget to check out the whole series.