A domain hack (sometimes known as a domain name hack) is an unconventional domain name that combines domain levels, especially the top-level domain (TLD), to spell out the full "name" or title of the domain. Well-known examples include blo.gs, del.icio.us, cr.yp.to, retou.ch, and goo.gl.

In this context, the "hack" represents a trick (as in programming), not an exploit or break-in (as in security).

Domains such as .as, .it, .me, .us, or .co (American Samoa, Italy, Montenegro, United States, or Colombia respectively) are easy to use as domain hacks because they correspond to short, simple dictionary words. Alternatively, a name is chosen so that the last few characters match an existing top-level domain, such as "inter.net", so that every character is used in forming the common name.

Domain hacks offer the ability to produce extremely short domain names. For example, blo.gs has a total of only five letters (versus blogs.com, at eight letters), as every letter is taken into account as the site's title.

This makes them potentially valuable as redirectors (like i.am, which redirects to FortuneCity's V3 service), as pastebins and as base domains from which to delegate subdomains. Also short domains are useful for URL shortening services.