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

Simplicity and openness are central to wikis: anyone can often add or change pages without technical knowledge, and edits are usually logged for review or rollback.

Main 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:** 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:** Wikis may allow public editing or restrict changes to registered or authorized users.
- **Discussion pages:** Separate talk pages allow contributors to discuss edits and structure.

Common uses
- Crowd-sourced knowledge resources (e.g., Wikipedia)
- Project docs and corporate knowledge repositories
- Group writing and collaborative note-taking
- Educational and classroom projects

Benefits
- **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.

Drawbacks
- **Vandalism and false information:** Open editing may allow intentional or accidental inaccuracies.
- **Inconsistent quality:** Content quality may vary widely between pages.
- **Organizational issues:** Poor coordination or governance can cause content fragmentation and disputes.

Example
- **Wikipedia** — the best-known wiki, run by the Wikimedia Foundation and built by volunteer contributors worldwide.