A crypto airdrop is when a blockchain project distributes free tokens or coins to the crypto community. To be a recipient of an crypto airdrop often the only requirement is that you have coins from the relevant blockchain stored in your wallet. Examples of this format of airdrops are Byteball, Stellar lumens and OmiseGo. The format of these crypto giveaways is usually like this: At a pre-announced time the project behind the event will take a ”snapshot” of the blockchain, and anyone holding Ether or Bitcoin at that point will receive a certain number of free tokens. This can also be done on other blockchains, but Ethereum and Bitcoin are the most used for this airdrop format. Currently the most commen crypto airdrops require a few simple social media task. These projects use an airdrop as a marketing campaign. Examples of this format are Shivom, TraXion and Sandblock. A Hardfork is a less common, but well known way to do an airdrop. At a certain block number a chain Hard fork's in to two separate chains. if both chains get miner and community support you now have 2 separate coins! The most famous examples of this are Bitcoin Cash & Ethereum Classic.