Token approval
In short A token approval is permission you give a smart contract to move a set amount of a token from your wallet, often needed before swapping or depositing.
On EVM chains like Ethereum, BNB Chain, and Base, a contract cannot pull ERC-20 tokens out of your wallet unless you approve it first. An approval, also called an allowance, tells the token contract that a specific spender address may transfer up to a set amount on your behalf. That is why a DEX asks you to approve a token before your first swap.
Technically you call approve(spender, amount) on the token contract, and it records the allowance. The spender can then call transferFrom whenever it likes, up to that amount, with no further confirmation from you. Many apps request an unlimited amount to save gas on future trades. Some tokens also support permit signatures, which create an approval through an off-chain signature instead of a transaction. Solana uses a delegate system that works along similar lines, though apps there more often move tokens within the same transaction you sign.
Approvals matter because they outlive the moment you granted them. If the approved contract is malicious, later exploited, or upgraded, it can take your tokens months after you used it. Wallet drainers and phishing sites rely on getting you to approve or sign a permit for your most valuable tokens.
Approve only the amount you need when the app allows it, and read the spender address and amount your wallet shows. Be extra careful with signature requests that mention permit, since they look harmless but grant access. Periodically review your active approvals with a block explorer's approval checker or a revoke tool and cancel ones you no longer use; revoking costs a small gas fee.