An Application Programming Interface (API) allows you to connect your code to eZ Platform.
From the eZ Blog: http://ez.no/Blog/How-would-you-explain-what-an-API-is-to-your-mom
eZ Platform offers two APIs:
- The REST API allows you to interact with an eZ Platform installation using the HTTP protocol, following a REST interaction model
- The Public (PHP) API exposes a Repository which allows you to create, read, update, manage and delete all objects available in eZ Platform, first and foremost content, but also related objects like sections, locations, content types, content types groups, languages and so on.
There is also a JavaScript API Client, useful for working with eZ Platform as a headless CMS.