Domain name
The address or URL of a particular Web site, it is the text name corresponding to the numeric IP address of a computer on the Internet.

IP address (Internet Protocol address)
A numeric address that is given to servers and users connected to the Internet. For servers, a Domain Name Server (DNS) translates it into a domain name. For users, the Internet Service Provider (ISP) assigns it when the user goes online. This IP address might be the same number each time the user logs on (static IP), or it might be a newly assigned number each time the user connects.

Domain Name System (DNS)
Every computer on the Internet has a unique address just like a telephone number, which is a string of numbers. It is called its IP address. But it is hard to remember everyone's IP address. The Domain Name System makes it easier by allowing a familiar string of letters (domain name) to be used instead of the IP address. Translating the name into the IP address is called resolving the domain name.

Top-level domain
In the Domain Name System (DNS) hierarchy, it is the highest level under the root. In a domain name, it is that portion that appears furthest to the right; for example, the com in www.cqcounter.com. There are a large number of top-level domain's, for example .biz, .com, .edu, .gov, .info, .int, .mil, .net, and .org.

Country code top-level domains (ccTLD)
Two letter domains, such as .uk, .de and .jp (for example), are called country code top-level domains (ccTLD) and correspond to a country, territory, or other geographic location. The rules and policies for registering domain names in the ccTLDs vary significantly and some are reserved for use by citizens of the corresponding country.

Second-level domain
In the Domain Name System (DNS) hierarchy, it is the highest level underneath the top-level domains. It is that portion of the domain name that appears immediately to the left of the top-level domain, separated by a dot. For example, the Anydomain in www. anydomain.com is a second-level domain.

Third-level domain
In the Domain Name System (DNS) hierarchy, it's the highest level underneath the second-level domains. It is that portion of the domain name that appears two segments to the left of the top-level domain; for example, the www in www. anydomain.com.

Whois
An Internet utility that returns information about a domain name or IP address. For example, if you enter a domain name such as anydomain.com, whois will return the name and address of the domain's owner.