Layer 2
In short A Layer 2 is a network built on top of a base blockchain that processes transactions off the main chain and settles them back to it for lower fees.
A Layer 2, or L2, is a separate network that runs on top of a Layer 1 and relies on it for final settlement. The goal is to handle many more transactions at lower cost than the base chain can, while still borrowing its security. Base, Arbitrum, and Optimism are well-known L2s on Ethereum, and the Lightning Network is a payment-channel L2 on Bitcoin.
The common design today is the rollup. The L2 executes transactions on its own, bundles them, and posts compressed data plus a proof or commitment to the L1. Because many transactions share the cost of one L1 posting, each user pays far less. If the L2 operator misbehaves, the data and proofs on the L1 are meant to let users challenge bad state or withdraw their funds directly.
For token buyers this matters in practical ways. A token on an L2 is a different contract from the same token on the L1, and moving between them requires a bridge, which can take minutes or, for some optimistic rollups, about a week for standard withdrawals. Many L2s still run a single sequencer that orders transactions, so it can go down or censor in the short term, and some have upgrade keys controlled by a small group.
Before buying on an L2, confirm the contract address on that specific network, keep a little ETH (or the required gas token) there for fees, and use official or well-established bridges. Check how mature the L2's security is: whether fraud or validity proofs are live, who can upgrade its contracts, and whether users can exit without the operator's cooperation. Cheap fees are nice, but they are not the same as strong security.