AppChains, short for application-specific blockchains, are blockchains that are dedicated to a specific application or use case. Unlike traditional blockchains like Bitcoin or Ethereum that serve multiple applications, AppChains focus on providing customized solutions for a particular application. This customization can include various aspects such as security models, fee tokens, write permissions, and more. AppChains can be implemented as monolithic blockchains or as modular execution layers like rollups, sidechains, or plasma chains. They offer developers the flexibility to tailor the blockchain infrastructure to meet the specific needs of their application, improving scalability, customizability, and user experience.