Admin Contact : This is the only person allowed to make changes to the domain. Ensure this Email address is always kept up-to-date.
Billing Contact : This is the contact responsible for billing issues with regard to this domain's registration. All renewal information will be sent to this address.
Technical Contact : This is the person who is normally responsible for Web hosting, mail, and other DNS issues for your domain. However, unless they are granted access by the Admin Contact, they have no authority to make any changes.