An Application Programming Interface (API) is a standardized way for different software systems to communicate and exchange information. APIs define the requests that can be made, how to make them, and the data formats used for responses. When you use a mobile app to check transit schedules, the app likely uses the transit authority's API to retrieve real-time data. Many Canadian governments provide public APIs as part of open data initiatives, allowing developers to build applications using government information about everything from weather to election results to building permits.