'Mintable' collections, like Rarible and Cargo, are collections where users are able to freely mint NFTs onto shared smart contracts.
The minting doesn't happen on OpenSea - we just show the available items and allow users to list them for sale. The 'mintable' warning icon is a yellow circle with an exclamation mark as shown below.
As with collections that haven't been safelisted, please do your research before making a purchase decision.
OpenSea reserves the right to remove these items before/after purchase if they are in violation of copyright laws or are known to be fake or inappropriate.