MetaMask is an augmentation for getting to Ethereum empowered circulated applications, or "Dapps" in your program!
The augmentation infuses the Ethereum web3 API into each site's javascript setting, so that dapps can peruse from the blockchain.
MetaMask likewise allows the client to make and deal with their own personalities (by means of private keys, neighborhood customer wallet and equipment wallets like Trezor™), so when a Dapp needs to play out an exchange and write to the blockchain, the client gets a protected interface to survey the exchange, prior to endorsing or dismissing it.
Since it adds usefulness to the ordinary program setting, MetaMask requires the consent to peruse and keep in touch with any website page. You can generally "see the source" of MetaMask the manner in which you do any Chrome augmentation, or view the source code on Github.