An internet fax API, or application programming interface, enables software developers to build applications that send and receive faxes using a web service. API uses a set of standard web protocols so that you can integrate your faxes into your existing software stack.
You can connect two systems using an API and allow them to communicate with each other. This communication can happen over the internet, within a single network, or even between different devices.
Think of an API as a bridge connecting two apps with each other. To illustrate, imagine a customer at a restaurant who places an order with a server. The latter then relays this to the food preparation staff. An API acts in a similar fashion.