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.

Key features
- **Collaborative editing:** Multiple people can edit the same pages, occasionally concurrently.
- **Edit history:** Each change is logged with a time and the editor’s name or IP.
- **Interlinking:** Creating links among pages is straightforward, which helps interconnect 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:** Separate talk pages allow contributors to discuss edits and structure.

Frequent uses
- Community knowledge bases such as Wikipedia
- Internal documentation and company knowledge bases
- Collaborative writing and shared note-taking
- Educational and classroom projects

Advantages
- **Fast collaboration:** Many people can collaborate and iterate quickly on content.
- **Openness:** Edit histories and talk pages reveal how content decisions were made.
- **Expandable:** Wikis expand easily as contributors add and organize content.

Drawbacks
- **Vandalism and false information:** Open editing may allow intentional or accidental inaccuracies.
- **Inconsistent quality:** Content quality may vary widely between pages.
- **Organizational issues:** Without clear governance, content may become fragmented or disputed.

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