The Layer 3 (L3) refers to an infrastructure layer built above second layer solutions (Layer 2) in the blockchain ecosystem. While Layer 1 (like Ethereum or Bitcoin) represents the base layer and Layer 2 enhances scalability with solutions like Optimism or Arbitrum, Layer 3 aims to facilitate specific use cases, such as creating specialized decentralized applications (dApps), blockchain games (GameFi), decentralized social networks, or interoperability between chains.

The goal of Layer 3 is to provide customizable environments, optimized for certain applications, while benefiting from the security of the underlying layers. These L3 are sometimes referred to as "app-chains" or "application-specific rollups", which allow developers to build tailor-made blockchains while relying on a modular architecture.