Wikis are websites built for collaborative authoring, allowing numerous contributors to add, edit, and structure content online.

They emphasize simplicity and openness — pages can be created or modified without special technical skills, and most maintain an edit history so revisions can be reviewed or reverted.

Main features
- **Collaborative editing:** Numerous contributors can work on pages, sometimes simultaneously.
- **Edit history:** Each change is logged with a time and the editor’s name or IP.
- **Interlinking:** It’s easy to create links between pages, forming an interconnected knowledge base.
- **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:** Dedicated discussion pages enable contributors to coordinate and discuss content.

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

Advantages
- **Fast collaboration:** Many people can collaborate and iterate quickly on content.
- **Openness:** Visibility into edits and discussions shows how decisions were reached.
- **Expandable:** They scale organically as users add more pages and topics.

Cons
- **Vandalism and false information:** Open contribution can result in deliberate or accidental misinformation.
- **Inconsistent quality:** Content quality may vary widely between pages.
- **Organizational issues:** Without clear governance, content may become fragmented or disputed.

Illustration
- **Wikipedia** — a well-known wiki operated by the Wikimedia Foundation and written by volunteers around the globe.