An Airdrop is an NFT or crypto marketing campaign where the developers of a project send a digital asset to selected wallet addresses on a blockchain. Its purpose is to publicize and add more value to a project. The condition for receiving an Airdrop depend on the side rules. While some might send you an Airdrop for completing a task, others reward you for holding a particular NFT or cryptocurrency.
Thus, an Airdrop can be exclusive, hard-forked, or standard.