Did you submit a swap or other transaction, and are still waiting for it to confirm?
Before assuming that the transaction is pending, there are 3 things to check:
1. Double check to see if the transaction is an Approval. Approvals are step 1 of 2 when using a token on 1inch for the first time, and do not actually move any tokens.
2. Check the block explorer. If the transaction shows as "Success", then you might need to simply add the token contract address to your wallet to see the funds.
3. If the transaction doesn't show up in the block explorer, it likely didn't broadcast to the network. In this case you will need to remove the stalled transaction and try again.
If your transaction doesn't apply to the above 3 scenarios, and the status shows "Pending" in the block explorer, there may be several reasons why it hasn't yet confirmed.
The transaction was sent with a low gas price. The order in which transactions are processed depends on the gas price you set: expensive transactions can get processed faster (minutes), and cheaper ones have to wait longer (sometimes days).
Several transactions are sent at once and the first transaction with a low price delays the current one. Please, read more here.
There are connectivity issues with your Ethereum wallet. Transaction is not broadcast to the internet. The easiest way to work around that issue is to reset the account.
E.g in MetaMask you have to go to Setting > Advanced > Reset Account. This would force MetaMask to forget your outgoing transactions. Then you can try again.
Pending Limit orders
If you have an active limit order (that hasn't been filled). Please see this article for more info.