It is a device that stores the private key outisde of your computer in a way that the private key itself is never send outisde of the device. This way, even if there is malware on your pc, they will never have access to the private key.
In addition, there is a pin on the device with a scrambled keypad that changes every time, making software that tracks your screen unable to tell what your pin is.
I think TREZOR are perfect for people that want to safely store their coins on an online pc AND want the convenience of being able to spend them without too much hassle.
it is a wallet.
a wallet just stores the privkey.. EG paperwallet.
the misconception is the wallet need to be the program.. but a wallet, just like that leather thing in your back pocket just stores the access to funds.(privkeys)
a wallet is just not a LITENODE like electrum/multibit which is a program that communicates AND has a wallet.
did you know core 0.13.1 is a full NODE, yet doesnt have the segwit wallet enabled.
inshort this means it doesnt let users make segwit keys. thus while segwit is not yet 'on the network' people cannot accidently make a segwit transaction which is deemed 'anyonecanspend' at the moment. core will release a new node implementation 'when they are happy' after activation that does include a functional segwit wallet (inshort able store of segwit keys)
as many have said in the past. bitcoin wallets doesnt store funds, so 'wallet' is a bad buzzword anyway. it should have always been called (for analogy purposes).. a keyring, you know the hoop of metal which 'secures and keeps keys together'