You've got definition of what an airdrop is.
I just want to remind everyone that's into airdrops that be careful of the airdrop you are joining. Many of them aren't true to what they say and likely to scam people, don't give them ETH/BTC if they are asking you to send them.
Even just with your own common sense you can able to find out that a project is fraud when they do ask out such matter. Airdrop is free and theres no such requirement for you to get those tokens.
I think airdrop is a coin that is distributed for free by a company to support their project. In following this airdrop you only have to register and set up a wallet that supports the tokens to be given.
Simple instructions which can anyone follow but the fact airdrops nowadays do even require sending funds and KYC procedure which is a total bullshit.