A wiki is a website designed for collaborative editing, letting many people create, update, and organize content directly in a web browser.

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.

Key features
- **Collaborative editing:** Several contributors can edit pages, sometimes at the same time.
- **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:** Wikis may allow public editing or restrict changes to registered or authorized users.
- **Discussion pages:** Talk or discussion pages let contributors debate edits and organization.

Frequent uses
- Community-driven knowledge bases (for example, Wikipedia)
- Internal documentation and company knowledge bases
- Group writing and collaborative note-taking
- School and instructional projects

Benefits
- **Fast collaboration:** Many people can collaborate and iterate quickly on content.
- **Openness:** Transparency through revision histories and discussions.
- **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.

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