An Auth-Code also known as an EPP code, authorization code, transfer code, or Auth-Info Code, is a generated passcode required to transfer an Internet domain name between domain registrars; the code is intended to indicate that the domain name owner has authorized the transfer.
Extensible Provisioning Protocol (EPP)
The Extensible Provisioning Protocol, or EPP, is a flexible protocol designed for allocating objects within registries over the Internet.
The motivation for the creation of EPP was to create a robust and flexible protocol that could provide communication between domain name registries and domain name registrars. These transactions are required whenever a domain name is registered or renewed, thereby also preventing Domain hijacking.