"TREZOR is an isolated environment for offline transaction signing and using a small display you can visually verify the transaction contents. That's why all operations using TREZOR are entirely safe." - quote from website.
The Trezor works via a Chrome extension in your browsers allowing access to your coins while keeping your private keys safely offline, secured on the Trezor. It also has a number of other layers of security and comes with a recovery process in case of loss or theft.