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:** All edits are stored with timestamps and the author’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:** 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.

Typical uses
- Crowd-sourced knowledge resources (e.g., Wikipedia)
- Project documentation and internal company knowledge repositories
- Collaborative writing and shared note-taking
- Classroom and educational projects

Advantages
- **Fast collaboration:** Multiple people can add and refine content quickly.
- **Openness:** Transparency through revision histories and discussions.
- **Expandable:** Wikis can grow naturally as contributors add new topics.

Cons
- **Vandalism and false information:** Public editing can lead to vandalism or incorrect information.
- **Inconsistent quality:** Articles can differ greatly in depth, tone, and reliability.
- **Organizational issues:** Lack of structure or rules can lead to disorganization and conflicts.

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