Overselling is where you can sell more than you have purchased.
Reseller 1 Package
Disk space 10gb
The amounts above give you the total resources available to you as a reseller So if you were to create a package with 1gb of disk space and 5gb of bandwidth then create 12 accounts then you would have promised to your customers a total of 12gb of disk space and 60gb of bandwidth this is overselling.
cPanel/WHM does not allow you to deliver on this promise with overselling, what would happen is once you have hit any of the Reseller 1 limits on either disk space or bandwidth then your account would stop serving the websites.
This would mean that if 10 of your customers hit their allowance and the other two only used 10% they too would be suspended! We dont allow overselling for this reason as resellers often get into trouble with this option, so we restrict you to what you have purchased so based on the above scenario you would only be able to create 10 accounts. So it would only be the accounts that go over their allowance that would be affected.