That’s a different thing: pre-authorization. It’s used for when you want to authorize some purchase before delivering the goods (that you later confirm once it’s delivered). The pre-auth is still done online for amounts above the card-offline limit.

The nicer feature of preauth is that you can confirm a lower amount. So in the case of a gas pump, they first have to make sure you have the money, without knowing how much, because you haven’t pumped it yet. Once you finish, then they know the amount, and confirm the transaction at a lower amount.