If you have chosen the following option in your List Settings:
Activate Double Opt-in for this list but continue sending to all subscribers
Then, when you select the View list, you will notice that a new column has appeared named: Double opt-in and the email address has the status Unverified.
There are different reasons why you can see this status.
i) The user has subscribed to your mailing list, but hasn't yet click on the verification link that was included in the Double Opt-in email that was sent.
ii) You have manually imported the subscriber either via the add member or via the other import methods (CSC, Excel, Copy/ Paste) and since you don't have the consent via a Double Opt-in process you haven't checked the checkbox.
In case you already have been given consent by other means, you may add a member as verified by ticking the respective checkbox below. Else, the owner of the added address will receive an email to confirm their subscription consent.