Uses and abuses

As domain names became attractive to marketers—rather than just the technical audience for which they were originally intended—they began to be used in manners that in many cases did not fit in their intended structure. As originally planned, the structure of domain names followed a strict hierarchy in which the TLD indicated the type of organization (commercial, governmental, etc.), and addresses would be nested down to third, fourth, or further levels to express complex structures, where, for instance, branches, departments and subsidiaries of a parent organization would have addresses that were subdomains of the parent domain. Also, hostnames were originally intended to correspond to actual physical machines on the network, generally with only one name per machine.
However, once the World Wide Web became popular, site operators frequently wished to have memorable addresses, regardless of whether they fit properly into the structure; thus, because the .com domain was the most popular and memorable, even noncommercial sites began to obtain domains in that gTLD, and sites of all sorts wished to have second-level domain registrations even if they were parts of a larger entity where a subdomain would have been logical (e.g., abcnews.com instead of news.abc.com). A website found at ''http://www.example.org'' will often be advertised without the http:// and, in most cases, can be reached by just entering example.org into a web browser. In the case of a .com, the website can sometimes be reached by just entering example (depending on browser versions and configuration settings, which vary in how they interpret incomplete addresses).
The popularity of domain names also led to uses which were regarded as abusive by established companies with trademark rights; this has become known as cybersquatting, in which a person registers a domain name that resembles a trademark in order to profit from visitors looking for that address. To combat this, various laws and policies were enacted to allow abusive registrations to be forcibly transferred, but these were sometimes themselves abused by overzealous companies committing reverse domain hijacking against domain users who had legitimate grounds to hold their names. Such legitimate uses could include the use of generic words that are contained within a trademark, but used in a particular context within the trademark, or their use in the context of fan or protest sites with free speech rights of their own.
Laws that specifically address domain name conflicts include the Anticybersquatting Consumer Protection Act in the United States and the Trademarks Act of 1999 in India. Alternatively, domain registrants are bound by contract under the UDRP to comply with mandatory arbitration proceedings should someone challenge their ownership of a domain name.

Top-level domains

Every domain name ends in a top-level domain (TLD) name, which is always either one of a small list of generic names (three or more characters), or a two-character territory code based on ISO-3166 (there are few exceptions and new codes are integrated case by case). Top-level domains are sometimes also called first-level domains.The generic top-level domain (gTLD) extensions are:v • d • eGeneric top-level domainsUnsponsored.biz · .com · .edu · .gov · .info · .int · .mil · .name · .net · .orgSponsored.aero · .asia · .cat · .coop · .jobs · .mobi · .museum · .pro · .tel · .travelInfrastructure.arpa · .rootProposedLocations.berlin · .lat · .nycChildren.kid · .kidsLinguistic.bzh · .cym · .gal · .scoTechnical.geo · .mail · .webOther.post · .xxxDeleted/retired.natoReserved.example · .invalid · .localhost · .testPseudo.bitnet · .csnet · .ip · .local · .onion · .exit · .uucpUnofficialAlternative DNS rootsCountry code top-level domainsThe country code top-level domain (ccTLD) extensions are:v • d • eCountry code top-level domainsActive: .ac .ad .ae .af .ag .ai .al .am .an .ao .aq .ar .as .at .au .aw .ax .az .ba .bb .bd .be .bf .bg .bh .bi .bj .bm .bn .bo .br .bs .bt .bw .by .bz .ca .cc .cd .cf .cg .ch .ci .ck .cl .cm .cn .co .cr .cu .cv .cx .cy .cz .de .dj .dk .dm .do .dz .ec .ee .eg .er .es .et .eu .fi .fj .fk .fm .fo .fr .ga .gd .ge .gf .gg .gh .gi .gl .gm .gn .gp .gq .gr .gs .gt .gu .gw .gy .hk .hm .hn .hr .ht .hu .id .ie .il .im .in .io .iq .ir .is .it .je .jm .jo .jp .ke .kg .kh .ki .km .kn .kp .kr .kw .ky .kz .la .lb .lc .li .lk .lr .ls .lt .lu .lv .ly .ma .mc .md .me .mg .mh .mk .ml .mm .mn .mo .mp .mq .mr .ms .mt .mu .mv .mw .mx .my .mz .na .nc .ne .nf .ng .ni .nl .no .np .nr .nu .nz .om .pa .pe .pf .pg .ph .pk .pl .pn .pr .ps .pt .pw .py .qa .re .ro .rs .ru .rw .sa .sb .sc .sd .se .sg .sh .si .sk .sl .sm .sn .sr .st .sv .sy .sz .tc .td .tf .tg .th .tj .tk .tl .tm .tn .to .tr .tt .tv .tw .tz .ua .ug .uk .us .uy .uz .va .vc .ve .vg .vi .vn .vu .wf .ws .ye .za .zm .zwCyrillic: .рф Reserved/unassigned: .bl .eh .mf Allocated/unused: .bv .gb .pm .sj .so .um .yt Phaseout: .su .tp .yu Deleted/retired: .cs .dd .zr Other-level domains In addition to the top-level, or root, domains, there are second-level domain (SLD) names. These are the names directly to the left of .com, .net, and the other top-level domains. As an example, in the domain en.wikipedia.org, wikipedia is the second-level domain.Next are third-level domains, which are shown immediately to the left of a second-level domain. In the en.wikipedia.org example, en is a third-level domain. There can be fourth- and fifth-level domains, and so on, with virtually no limitation. An example of a working domain with five levels is www.sos.state.oh.us. Each level is separated by a dot, or period symbol.Domains of third or higher levels are also known as subdomains, though this term technically applies to a domain of any level because even a top-level domain is a "subdomain" of the "root" domain (a "zeroth-level" domain that is designated by a dot alone).Traditionally, the second-level domain has been chosen based on the name of a company (e.g., microsoft.com), product or service (e.g., productservice.com). The third level was commonly used to designate a particular host server. Therefore, ftp.wikipedia.org might be an FTP server, www.wikipedia.org would be a World Wide Web server, and mail.wikipedia.org could be an email server. Modern technology allows multiple servers to serve a single subdomain, or multiple protocols or domains to be served by a single computer. Therefore, subdomains may or may not serve any real purpose.