A top-level domain (TLD) is the highest level of domain name system which is the most often used. Common TLDs include .com, .com, and .org. For example, in the domain name www.example.com, the top-level domain is com.
Reserved Top Level DNS Names
To reduce the likelihood of conflict and confusion, a few top level domain names are reserved for use in private testing. The following four top-level domain names have been reserved by the Internet Assigned Numbers Authority (IANA).
.test, .example, .invalid and .localhost
- example: reserved for use in examples
- invalid: reserved for use in obviously invalid domain names
- localhost: reserved to avoid conflict with the traditional use of localhost as a hostname
- test: reserved for use in tests
Second-level domain (SLD) names
Names directly to the left of .com and the other top-level domains. For example, in the domain name www.example.com, the second-level domain name is example.
Second-level domains will refer to the organization that registered the domain name.
Third-level domains
Written immediately to the left of a second-level domain. For example, in the domain en.wikipedia.org, wikipedia is the third-level domain name is en.
ccTLD, gTLD
ccTLD – country code top-level domains : Based on the two-character territory codes of ISO-3166 country abbreviations.
gTLD – generic top-level domains : Represented a set of categories of names and multi-organizations.[2] These were the domains GOV, EDU, COM, MIL, ORG, NET, and INT