Application Programming Interfaces (APIs):
Application Programming Interfaces (APIs) are an advanced method of connecting your site to other websites or services online. You can get almost anything done if a service you want to use has an API. This is about as advanced as you can get, so if you don’t know what an API is, or don’t know what service specifically you want to use on your site, you probably don’t need this. Please note that this option is included for custom sites only.