Airdrop
An airdrop is a token handout. A project sends coins to wallets of people who did something: used the service, held a token, joined a list. It grabs attention and shares a slice with the community.
Only the name is free. You pay with time, attention and sometimes network fees. The real danger is fakes: scammers clone handouts to reach your wallet.
You have used a DeFi service for a while and it announces a handout for early users. Open the site only from a link in the official account of the project. If a link lands in your DMs from "support", treat it as a trap.
What not to do
Never type your seed phrase to "claim an airdrop" and do not approve unclear permissions in your wallet. A real handout asks for neither. Do not send your own tokens "for verification".