When you send a Bitcoin transaction, you send an output from a former transaction, becoming an input of a new transaction. When the output of a transaction is used as the input of another transaction, it must be spent in its entirety. Sometimes the coin value of the output is higher than what the user wishes to pay. In this case, the client generates a new Bitcoin address, and sends the difference back to this address. This is known as change. See https://en.bitcoin.it/wiki/Change to know more about this important Bitcoin protocol topic.
These operations are normally calculated and done all-in-once when you send a transaction from your Ledger wallet. In some cases, a minor bug can make these outputs visible on your device, requiring 2 authentication on your side instead of one. If 2 outputs are displayed on your Ledger device, the second output (Output #2) is the one corresponding to your change address, to send the rest of your bitcoins to yourself.
If this happens, it is likely because you use a Segwit address with an old version of the Chrome application, not adapted to Segwit.
If so, you need to update your Chrome application by removing and reinstalling it:
In your Chrome browser go to chrome://extensions/
Click on the bin below "Ledger Wallet Bitcoin"
Click on the "Add to Chrome" blue button and launch it again