A unique designator on the Internet made up of symbols separated by dots, such as

This.is.a.sample.domain.name.com

The individual words or characters between the dots are called labels. The label furthest right represents the top level domain, com, org, uk and so on. The second most right represents the second level of domain, or "second level domain."

Other terms are child and parent.

Scrooge.com is the parent of Cratchet.Scrooge.com
Scrooge.com is the child of com.

There are certain rules required in domain name creation.

• There can be no more then 127 labels.
• No label can be longer then 63 characters.
• Labels are made up of letters, numbers and hyphens, and may not start with hyphens.
• Labels are case insensitive.
• A domain name must be defined in its closest ancestral zone (The one with the most labels).