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

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.

Common 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:** Links between pages are simple to create, helping build connected content.
- **Lightweight markup:** Formatting is usually handled by lightweight markup languages (e.g., WikiText or Markdown).
- **Permission settings:** Access controls vary — from fully open editing to permissions for certain users or groups.
- **Discussion pages:** Dedicated discussion pages enable contributors to coordinate and discuss content.

Common uses
- Community knowledge bases such as Wikipedia
- Project docs and corporate knowledge repositories
- Cooperative writing and shared notes
- 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 can grow naturally as contributors add new topics.

Drawbacks
- **Vandalism and false information:** Open contribution can result in deliberate or accidental misinformation.
- **Inconsistent quality:** Articles can differ greatly in depth, tone, and reliability.
- **Organizational issues:** Lack of structure or rules can lead to disorganization and conflicts.

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