https://blog.trezor.io/how-does-segregated-witness-work-in-trezor-wallet-e8dd34d0fc1a
This guide for TREZOR Wallet is coin-agnostic, meaning it applies to all Bitcoin-like cryptocurrencies, which are supported in the Wallet and have implemented Segregated Witness (SegWit). Currently, these are: Bitcoin and Litecoin.
TREZOR Wallet will support both standard and legacy accounts indefinitely.
What is a standard account?
A standard account is the default account in your Wallet, benefiting from all SegWit-related features. As such, they use a new address format (P2SH), to differentiate themselves from legacy accounts and their addresses.
If you decide to use standard accounts, you can expect these positive changes:
Faster signing process for larger transactions
Cheaper transactions
More information available here.
Bitcoin’s standard accounts have addresses that start with 3 .
Litecoin’s standard accounts have addresses that start with M or 3 .
What is a “Legacy account”?
Legacy accounts are your old accounts from before SegWit activated. Your coins, as well as the entire account history, can be found in your legacy accounts.
The legacy accounts are fully functional, albeit they cannot benefit from SegWit-related features, available only in the standard accounts.
Bitcoin’s legacy addresses start with 1 .
Litecoin’s legacy addresses start with L.
Some third party applications will only work with your legacy accounts for now until they implement SegWit support.