The Site API is a general access gateway into the majority of the platform's api functionality.
This API exposes two levels of access privileges ( public and private ). Depending on the context/action for the API call only certain operations will be available for the public access level. All API functionality will be available for the private access level.
The public API key does not have to be kept private. However the private API key has full privileges to the API and should only be given out to developers/individuals who should have access to the full functionality of the API.