Internal name

Definition
An internal name is

"a domain or Internet Protocol (IP) address that is part of a private network. These internal names are not allocated to any specific organization and therefore cannot be verified. Common examples of internal names are:
 * Any server name with a non-public domain name suffix. For example, www.company.local or server1.company.corp.
 * NetBIOS names or short hostnames, anything without a public domain. For example, Web1, ExchCAS1, or Frodo.
 * Any IP address in the RFC19181 range. These addresses are reserved for private networks only."

Overview
"Internal names are not verifiable by CAs because it is not possible to look up who owns them. When determining whether a certificate application is for internal use or not, CAs often rely on the list of currently delegated Top Level Domains (TLDs) and not, for instance, against the list of the TLDs applied for in ICANN’s new Generic TLD (gTLD) program. For instance, although www.exampletld is currently an internal name, exampletld could be an applied-for-TLD and www.exampletld may later become operational."