What is an API?

API stands for application programming interface, and an API is a defined way in which two applications can interface with each other and can be thought of as an agreed contract. A good analogy for APIs is an electrical plug socket. Whichever country or region of the world you are in, there will be a defined standard for how electricity is provided from the national power grid to your socket. Every manufacturer of an electrical good in the region knows that when their appliance or device is plugged into the socket, it will receive electricity at a set frequency and voltage. In this instance, the design of the socket and the frequency and voltage of the electricity from it provide the API for the electrical grid.

The power of having a well-defined API such as this is that it makes it very easy for people to integrate with your solution without the need for a lot of custom overhead. For example, Salesforce provides a suite of very well-defined and documented APIs for...