An airdrop is when a project distributes free tokens to a set of wallet addresses — often people who already used an earlier version of the product, held a related asset, or met some other criteria. Legitimate airdrops are a genuine marketing and community-building tool.
Airdrops are also a very common scam vector: fake "claim your airdrop" sites trick people into connecting their wallet and approving a malicious transaction, or into entering their seed phrase directly. A genuine airdrop never requires your seed phrase, and claim links are always worth verifying independently before connecting a wallet.