Wikis may exist to serve a specific purpose, and in such cases, users use their editorial rights to remove material that is considered "off topic." Such is the case of the collaborative encyclopedia Wikipedia. In contrast, open purpose wikis accept content without firm rules as to how the content should be organized.

Ward Cunningham, the developer of the first wiki software, WikiWikiWeb, originally described it as "the simplest online database that could possibly work." "Wiki" (pronounced [ˈwiti] or [ˈviti]) is a Hawaiian word for "fast".

WikiWikiWeb was the first wiki. Ward Cunningham started developing WikiWikiWeb in 1994, and installed it on the Internet domain c2.com on March 25, 1995. It was named by Cunningham, who remembered a Honolulu International Airport counter employee telling him to take the "Wiki" shuttle bus that runs between the airport's terminals. According to Cunningham, "I chose wiki-wiki as an alliterative substitute for 'quick' and thereby avoided naming this stuff quick-web."

Cunningham was in part inspired by Apple's HyperCard. Apple had designed a system allowing users to create virtual "card stacks" supporting links among the various cards. Cunningham developed Vannevar Bush's ideas by allowing users to "comment on and change one another's text."

In the early 2000s, wikis were increasingly adopted in enterprise as collaborative software. Common uses included project communication, intranets, and documentation, initially for technical users. Today some companies use wikis as their only collaborative software and as a replacement for static intranets, and some schools and universities use wikis to enhance group learning. There may be greater use of wikis behind firewalls than on the public Internet.

On March 15, 2007, wiki entered the online Oxford English Dictionary. Some people claim "Wiki" also stands for "What I Know Is" but this is a false backronym.

Ward Cunningham and co-author Bo Leuf, in their book The Wiki Way: Quick Collaboration on the Web, described the essence of the Wiki concept as follows:

A wiki enables communities to write documents collaboratively, using a simple markup language and a web browser. A single page in a wiki website is referred to as a "wiki page", while the entire collection of pages, which are usually well interconnected by hyperlinks, is "the wiki". A wiki is essentially a database for creating, browsing, and searching through information. A wiki allows for non-linear, evolving, complex and networked text, argument and interaction.

A defining characteristic of wiki technology is the ease with which pages can be created and updated. Generally, there is no review before modifications are accepted. Many wikis are open to alteration by the general public without requiring them to register user accounts. Sometimes logging in for a session is recommended, to create a "wiki-signature" cookie for signing edits automatically.[citation needed] Many edits, however, can be made in real-time and appear almost instantly online. This can facilitate abuse of the system. Private wiki servers require user authentication to edit pages, and sometimes even to read them.

Boulous et al. write that it is the "openness of wikis that gives rise to the concept of 'Darwikinism', which is a concept that describes the 'socially Darwinian process' that wiki pages are subject to. Basically, because of the openness and rapidity that wiki pages can be edited, the pages undergo an evolutionary selection process not unlike that which nature subjects to living organisms. 'Unfit' sentences and sections are ruthlessly culled, edited and replaced if they are not considered 'fit', which hopefully results in the evolution of a higher quality and more relevant page. Whilst such openness may invite 'vandalism' and the posting of untrue information, this same openness also makes it possible to rapidly correct or restore a 'quality' wiki page."