Layer 2 (L2) is a collective term for off-chain scaling solutions that inherit the security of a Layer 1 blockchain while processing transactions faster and cheaper. Major categories include Optimistic Rollups (Arbitrum, Optimism) and ZK Rollups (StarkNet, zkSync).
Proof of Work (PoW) is the original blockchain consensus mechanism, made famous by Bitcoin. Miners compete to solve computationally expensive puzzles to validate transactions and add blocks to the chain. The difficulty automatically adjusts to maintain consistent block times.
Chainlink is the leading decentralised oracle network, providing smart contracts with secure access to real-world data, APIs, and external computation. It is the essential infrastructure layer connecting blockchains to off-chain information such as stock prices, weather data, and sports results.