I defined about metamask.
MetaMask is a web wallet that uses a browser extension that can store Ethereum and ERC20 compliant Ethereum tokens.
By using this wallet, you can connect the web page and the Ethereum protocol (blockchain).By connecting, you can send and receive Ether and ERC20 tokens from your browser.
However, since the private key is managed online, it is not recommended to store a large amount of Ether or ERC20 tokens. If you want to store it strictly, use a hardware wallet or the like.
MetaMask can also connect to the testnet as well as the mainnet, making it an indispensable tool for developers if they want to develop something with Ethereum.