Hi @machoman69,

I hope you are well today and thank you for your question.

There is a concept of parent and child theme in WordPress. The gillion zip file is a parent theme and  gillion child zip is a child theme.

You can get more information about this on the below page.

http://freewptp.com/why-and-how-to-create-wordpress-child-theme/

Best regards,
Shufflehound team