In a split DNS infrastructure, you create two zones for the same domain, one to be used by the internal network, the other used by the external network typically users on the Internet. Split DNS directs internal hosts to an internal domain name server for name resolution and external hosts are directed to an external domain name server for name resolution.
Recommended Reading: Webopedia’s DNS definition.
Examples of Split DNS
Common reasons for using split DNS systems is to hide internal information from external clients on the Internet or to allow internal networks to resolve DNS on the Internet.