This document discusses APIs (Application Programming Interfaces) and how they allow software applications and online services to communicate. APIs are sets of routines, protocols, and tools that allow programs to interact with each other. They transmit data between devices in agreed-upon formats. APIs were initially created to make programming easier by providing reusable building blocks, and now allow things like embedding files from services like SlideShare onto blogs through web APIs. APIs are important because they enable connections and sharing of information between programs and online services.