Layer 2, also known as the Data Link Layer, is the second level in the seven-layer OSI reference model for network protocol design. And Layer 1 is about the public chains of Bitcoin network and Ethereum network.
Layer 2 Scaling Solutions is abbreviated as Layer 2, which is a term for a series of off-chain scaling solutions. These solutions will not affect the public chain itself since they are improved by off-chain improvement.
Taking Bitcoin network as an example, the Bitcoin Lightning Network is its Layer 2. However, Ethereum network has more Layer 2 projects such as Polygon, Arbitrum One, zkSync, ZKSwap, Loopring, xDAI, Optimistic Ethereum, etc. When the performance of Layer 1 (low TPS, high GAS fee, etc.) is not enough to meet user needs, there is a room for Layer 2 to deploy.