This are a set of protocols, tools, codes used for building software application. It provides the building block or a bridge to make software by using capabilities of other already available software. It can be used for integration of other elements to the program. The interface allows the integration of software i.e. a software can communicate to their software’s.
APIs are quite useful in today's world. Many big companies make available their APIs so that other developers can directly call or use them in their application to either speed up the development or get data from their databases.
e.g. In trading this enables a user to get connected with the market and facilitates real time sharing of data and trade execution.
This is highly reliable and fast, unlike the open cry trading used earlier. Almost all the trading bourses use API and uses its reliability as a selling point. In terms of volumes handled today, API is imperative and provides easy accessibility to wide number of users. They provide price quotation, trade execution, order entry and confirmation and other such features.