"Confirmed" field for mailing list

I am trying to import subscribers for a mailing list and noted the “confirmed” field is mentioned. What does this mean? There is no documentation on it.
How can I enter the subscribers as “confirmed” (whatever this means) upon exporting other mailing lists I noted some have a “0” and others are empty

Not sure what does it mean. But corresponding field can be found here


The newsletters may have Autoresponders, that can be used to confirm subscription. So in case when user clicks on the activation_link from such a subscription confirmation, this field will be updated in the database.

So in case there exist autoresponder and this autoresponder selected for the mailing list, customers will have to confirm their subscriptions firstly.