Decentralized finance (commonly referred to as DeFi) is an experimental form of finance that does not rely on financial intermediaries such as brokerages, exchanges, or banks, and instead utilizes blockchains, most commonly the Ethereum blockchain.
Metamask is an Ethereum wallet that allows you to interact with Curve and other dapps. You can also use it with Ledger and Trezor hardware wallets. It's the most popular Ethereum web wallet and is available as an add-on for most browsers.
Metapools are a type of pool on Curve composed of one asset as well as as LP tokens from another pool.
Yearn Protocol is a set of Ethereum Smart Contracts focused on creating a simple way to generate high risk-adjusted returns for depositors of various assets via best-in-class lending protocols, liquidity pools, and community-made yield farming strategies on Ethereum. It was founded by Andre Cronje who has been a long term collaborator of Curve Finance.
yCRV is not wrapped CRV, it's a wrapped representation of ownership of yUSDC+yUSDT+yDAI+yTUSD deposits in the Curve Y pool (i.e. your share of the pool). Each pool on Curve has an LP token with a different name.
yUSD (also yyCRV)
Yearn token wrapper that represents shares of the Y pool inside the Yearn Y Pool vault. It is a wrapped version of yCRV.