A Crypto Airdrop is a free giveaway. It's a common practice for new blockchain projects to distribute cryptocurrencies (also called coins or tokens) for free.
Each airdrop will require different tasks. In return, you usually have to complete some simple social media tasks, subscribe to their newsletter, or register on their website.
Those are called bounty airdrops.
There's also other types of airdrops like Holder airdrops and Forked airdrops but most of the airdrops we share are bounty airdrops.