In the context of Bitcoin, an output contains instructions for sending bitcoins. Value is the number of Satoshi (1 BTC = 100,000,000 Satoshi) that this output will be worth when claimed. For more information, see this external article.
To make the user experience better and easier, Trezor Wallet calculates all the inputs and outputs and displays only the final balances and transaction amounts. For more information about Trezor Wallet and transactions, see Understading transaction details.