In the context of Ethereum smart contract applications, external adapters in Chainlink provide flexibility and functionality beyond the native core adapters, allowing developers to connect smart contracts to premium web APIs and perform off-chain computations. These adapters facilitate the integration of high-quality data and are key to enhancing interoperability and performance, particularly when dealing with private APIs, low latency, high throughput computations, and cross-blockchain data writing. Building an external adapter can be simplified by creating a customizable API, which can be hosted by third-party node operators to maintain decentralization while allowing developers to focus on business logic. The process involves configuring requests and parameters to handle specific data, such as cryptocurrency prices or weather data, and ensuring secure API key management. External adapters empower smart contracts to become more intelligent and interconnected, with potential applications in various domains, including finance and data retrieval, as demonstrated through examples like fetching Ethereum prices or weather information.