Deleted/Inactive Users

New to Zoho and testing out the functionality and trying to understand how it works.

1) is the online documentation somewhere that explains how user accounts work? So far it has been confusing to me?

2) Conducted the following:

Created a new user from the company panel
logged in as that user and created the user id - sysadmin99
went back to company panel and deleted that user - sysadmin99
next tried to added another user and tried to reuse the id sysadmin99 on login

It told me that the user id sysadmin99 was already in use.

I then went back to the normal zoho login page and tried to login as sysadmin99 and it told me the user was inactive.

What does inactive mean?
Will I eventually be able to reuse that user id?

Thanks