Application interfaces, often referred to as APIs (Application Programming Interfaces), are sets of rules and protocols that allow different software applications to communicate with each other. They define the methods and data formats that applications can use to request and exchange information, enabling seamless integration and functionality across various systems. In simpler terms, an application interface acts like a bridge between different software programs, allowing them to work together. For example, when you use a social media app to share a photo, it may use an API to send that photo to a cloud storage service, ensuring that the data is transferred correctly and efficiently.