An API, or Application Programming Interface, specifies how two systems (websites, tablets, computers) communicate with one another. In this integration, there is a server and a client. Let’s apply this to something familiar. In this example, there’s a takeout restaurant with an online ordering system. In this scenario, you (the customer) are the client because you are placing an order, i.e. submitting a request. The restaurant is the server because they provide the API, i.e. the system for you to send an order. As a client, you can also make requests to the server to get, post new data, update or delete information.
For further reading, we recommend Zapier’s API reference