Token approvals authorize a smart contract to transact with your tokens. When you transact with a non-native token (ERC-20s or NFTs) you will need to approve tokens.
There are 2 types of token approvals, specific amounts or infinite. Approving specific amounts of tokens are like the name suggests, you will determine the amount of tokens you are allowing the smart contract to transact with (ie. 100 USDC). Infinite approvals allow the smart contract to transact with the entire token balance of the approved token until you manage your approvals and revoke allowances.
On Zapper, this will be needed when using the Swap or Bridge feature. By default, token approvals are set to specific amounts but this can be changed in the transaction settings.
Note: Token approvals are an extra transaction that does cost gas.