In the world of crypto, an airdrop is a marketing stunt, in which tokens or coins are sent out to blockchain wallets. Most commonly, it is done to promote a new token or cryptocurrency.
Usually, this is done without any cost to the receiver. Sometimes, this is done at random, or recipients are specifically selected after an initial promotion of the upcoming airdrop.
Recipients may be required to do something to promote the digital asset themselves, such as a retweet. Airdropping explored in popularity during the crypto coin boom of 2017.