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.

Common features
- **Collaborative editing:** Multiple people can edit the same pages, occasionally concurrently.
- **Edit history:** All edits are stored with timestamps and the author’s name or IP.
- **Interlinking:** It’s easy to create links between pages, forming an interconnected knowledge base.
- **Lightweight markup:** Simple markup languages (such as WikiText or Markdown) are used to format pages.
- **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.

Typical uses
- Community knowledge bases such as Wikipedia
- Internal documentation and company knowledge bases
- Cooperative writing and shared notes
- 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 can grow naturally as contributors add new 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:** Lack of structure or rules can lead to disorganization and conflicts.

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