API specifications are detailed documents that outline how different software applications can communicate with each other. They define the methods, data formats, and protocols that developers must follow to ensure seamless interaction between systems. This helps in creating consistent and reliable interfaces for applications. These specifications often include information about endpoints, request and response formats, authentication methods, and error handling. By adhering to these guidelines, developers can build applications that effectively utilize APIs, such as those provided by Google, Twitter, or Facebook, enhancing functionality and user experience.