Google API (Google Application Programming Interface) is a set of programming libraries made available by Google for (mobile and other) application developers can access Google Services (Google Docs, Google Calendar, Google Push Notifications, etc), or simply extend the functionality of their programs using code written by other developers. The developer embeds call to the Google API into their code, and makes calls to https://googleapis.com.

This SonicWALL signature identifies legitimate HTTPS traffic to Google APIs.