A secondary protocol or layer that is built on top of, or linked to a Layer 1 blockchain network for improved performance.
Since Layer 1 networks, such as Bitcoin and Ethereum focus on decentralization and security first, they suffer from scalability issues that prevent high transaction throughputs.
To solve these issues, developers build Layer 2 protocols on top of Layer 1 networks, offloading some of the network’s usage via various methods. The end-goal of these protocols is to improve scalability without sacrificing security.