What is an inactive user (and an active user) ?

When you are in your admin panel to find a user, you can see at the top of the window something like this :
Quote:

Active users are people who have registred to your website and who have clicked on the activation's key received by email.
Inactive users are people who have registred on your website but who did not clicked on the activation's key.

This Q&A was found on XOOPS Web Application System : https://xoops.org/modules/smartfaq/faq.php?faqid=312