Sometimes airdrop is a free giveaway of coins, based on how many bitcoins in your offline wallets (you have your own private key), by referring on certain block.
Such as bitcore, bitcoin cash...
For example, if you have 1 bitcoin, when bitcoin network is at blockheight 463604, you can claim free bitcore coin (btx).
Bitcore, not bitcoin core.
How can they send coins based on bitcoin addresses? Do they send coins to that same address, but in bitcore, and then one will need to use the same process as eg, when the bitcoin cash split occurred (send btc to a new wallet, use the previous private key to claim bitcoin cash)?
Sorry if my explanation make anyone confuse about bitcore airdrop. Please check website bitcore.cc for more explanation about bitcore.