An Application-Programming-Interface (API) is an interface that serves the unified and structured data transmission between different applications.
APIs are usually published as a part of a software development kit or are available as open API on the internet. The purpose of publishing APIs is to make them accessible for third party developers. So instead of implementing certain standard functions on their own, app developers can save a lot of work and time by simply using existing API solutions.
Whether social networks, productivity solutions, or business applications: successful online services or applications often have open APIs. These interfaces enable third party developers to access the data and functions of those applications. This way, developers can simply integrate these functions into their software instead of implementing them on their own. Considering this, APIs are empowering collaborative applications and thus the development of mashup-services and new applications.
Owing to the rapidly growing number of private and open APIs, a whole new business has evolved in the digital marketplace. Tech companies are not only serving consumers or business consumers anymore. Instead, more and more companies started to sell well documented interfaces to app developers. This growing business is called business-to-developer (B2D) and is existing next to the conventional business-to-consumer (B2C) or business-to-business (B2B) markets.