A wiki is a website designed for collaborative editing, letting many people create, update, and organize content directly in a web browser.

Wikis prioritize ease of use and openness: pages can be added or changed without technical expertise, and most track every edit so changes can be reviewed or undone.

Main features
- **Collaborative editing:** Numerous contributors can work on pages, sometimes simultaneously.
- **Edit history:** Every modification is recorded with a timestamp and the editor’s identity or IP address.
- **Interlinking:** Links between pages are simple to create, helping build connected content.
- **Lightweight markup:** Pages are typically formatted with lightweight markup like WikiText or Markdown.
- **Permission settings:** Some wikis are open to anyone; others limit edits to registered users or specific groups.
- **Discussion pages:** Talk or discussion pages let contributors debate edits and organization.

Common uses
- Community knowledge bases such as Wikipedia
- Internal documentation and company knowledge bases
- Group writing and collaborative note-taking
- School and instructional projects

Advantages
- **Fast collaboration:** Contributors can rapidly create and improve content.
- **Openness:** Visibility into edits and discussions shows how decisions were reached.
- **Expandable:** Wikis expand easily as contributors add and organize content.

Cons
- **Vandalism and false information:** Public editing can lead to vandalism or incorrect information.
- **Inconsistent quality:** Content quality may vary widely between pages.
- **Organizational issues:** Poor coordination or governance can cause content fragmentation and disputes.

Example
- **Wikipedia** — the largest example, maintained by the Wikimedia Foundation and contributed to by volunteers worldwide.