Layer 2 solutions are blockchain protocols built on top of existing blockchains (like Ethereum) to improve scalability and reduce transaction costs. Examples include rollups and state channels. This term is used by blockchain developers and those working on scaling solutions. To excel in Layer 2 development, one should understand the underlying blockchain's architecture, be familiar with different Layer 2 technologies and their trade-offs, and be able to design and implement efficient off-chain systems that maintain security guarantees.