Why is my transaction "pending"?

A transaction with a status of "pending" means that your transaction has been sent to the network but it is not yet included in the blockchain, or it does not have enough confirmations yet.
Both incoming and outgoing transactions can be "pending" until they have been successfully confirmed on the blockchain.

The BitBoxApp shows a transaction as "pending" until it has 6 confirmations.

How long does it take until your transaction is included in the blockchain depends on the chosen fee level. What are Bitcoin network fees?

For an estimate of how long it will take for the transaction to be added to the blockchain, enter your transaction ID in this Blockchain Explorer. You will see an ETA (Estimated Time of Arrival): https://blockstream.info/

If you are experiencing issues with an ETH transaction that shows "pending" for a very long time, please see here.