A legitimate airdrop rewards people who used a protocol early or held a related token. The project sends tokens directly to qualifying wallets, and you can usually verify it through the project's official channels. These are real and sometimes valuable.
The scam version wears the same clothes. A token appears claiming to be an airdrop, but claiming it means visiting a site and approving a contract. That approval is the whole point of the operation. The token has no value; your signature does. Treat any airdrop that requires you to connect and approve before you can see it as hostile until proven otherwise.
Verify before you touch. Confirm the airdrop through the project's known accounts, never through a link in the token name. If you cannot verify it, leave it alone. An unrequested token in your wallet is closer to dust than to a gift.