Zoho WorkDrive API Users

Zoho WorkDrive API Users

I notice that the Zoho WorkDrive API makes reference to "external users", 7 instances of it to be exact.

What is Zoho's definition of an "external user" in the context of the Zoho WorkDrive API?

Is it someone that must have a Zoho account?

And can you share a file with someone who does NOT have a Zoho account?