The billing contact is the person or organization responsible for handling any payment issues related to your domain name. This includes renewal notices and account reminders. The billing contact could be you or someone from your accounts department. You can have a different billing contact for each domain in your account. This way you can have different people manage the payment for their domain. Or you can set the billing contact to be your own for each domain.
The billing contact will receive the tax receipt for transactions related to this domain name. However, the billing contact will not receive any correspondence containing your account number or password.
If you need to update your domain’s billing contact, please see: How do I update my Account and Domain Contacts Information?