A whitelist is a list of accounts that you follow, and that you don’t want to unfollow by mistake or keep a close eye on them. We don’t show them in the Non-Followers page, even if they don’t follow you back.
To access your Whitelist, you need to go to your Audience menu, then click on the “Whitelist” tab and select the Twitter profile you want to view the Whitelist for.
In your whitelist, you’ll be able to view all of the accounts you’ve previously whitelisted, so the accounts you wanted to keep safe at some point in the past.
You can always remove an account from your Whitelist by clicking the big red button next to it. You can also add a particular Twitter handle if you know you don’t want to unfollow that person by adding the handle and then pressing “+ Add”.