Many sites tell you about their Application Programming Interface (APIs), starting with the stock exchange sites. In this case, it is neither the Isolated Parent Allowance nor an Important Punctual Alcoholization.
An API is a standardized set of classes, methods, or functions that serves as a facade via which it provides services to other software. APIs, public or private, all exist for the same reason. They facilitate new developments based on existing applications. They can take different forms, from web services to access the features of a site, all the way to the software library that integrates software into different development scenarios.
We can use APIs when data is changing quickly, like with stock prices. It doesn’t really make sense to regenerate a data set and download it every minute since it takes up a lot of bandwidth and is a slow process. Since APIs facilitate the communication between the programming language and other software, there is no need to know the program you want to exploit. Knowing its API is enough.
APIs often come with accurate documentation that saves a lot of time. This is also great for API developers, since they can easily modify or upgrade without affecting users in real-time. As long as the functions offered by the API always return the same information, their processing can change without affecting users.
Google is a major API provider, which is one of the reasons why their applications have gone mainstream. Many developers currently rely on their services, most of which are offered free of charge, to design theirs. Thus you will often find websites or programs (including SaaS software) using the Google services without your knowledge or permission.