.biz is a generic top-level domain intended for domains to be used by businesses; the name is a phonetic spelling of the first syllable of "business". It was created to relieve some of the demand for the finite domain names available in the .com top-level domain, and to provide an alternative to businesses whose preferred .com domain name had already been registered by another party. There are no specific legal or geographic qualifications to register a .biz domain name, except that it must be for "bona fide business or commercial use" (i.e. no personal or "soap box" sites, and no cybersquatting), and the usual legal remedies for trademark infringement are applicable. It was created in 2001 along with several others as the first batch of new gTLDs approved by ICANN following the boom in interest in the internet in the 1990s. It is administered by Neulevel.

In contrast to the sunrise period of .info, .biz did not grant trademark owners first chance at registration, but instead used a procedure whereby they could file intellectual property claims in advance and then challenge any eventual registrant through a policy named "STOP" (Startup Trademark Opposition Policy). A number of domains were successfully obtained by trademark owners from other registrants through this policy; some of the more controversial cases, where generic words were taken over based on trademark claims in a process deemed "reverse hijacking" by critics, included that of paint.biz and canadian.biz, the latter of which was later reversed by a court decision.

Although intended to be a restricted domain aimed at businesses, in reality the .biz domain is run as an unrestricted domain, available to anyone for any use. No enforcement mechanisms are planned or intended, at least directly by the registry or registrars, though it is in theory possible for third parties to challenge noncompliant registrations through a dispute resolution policy.

Although many .biz registrations have taken place (second only to .info among the new TLDs), critics note that it still has low name recognition with the general public, little use by major reputable businesses, and much use in spam, scams, and porn.