A wiki is a website that allows for collaboration and sharing of files like text, images, videos and presentations. Wikis allow multiple users to work together simultaneously. They can be public, private, or protected. Wikis are used to share files, communicate for group projects, and conduct surveys. To start a wiki, you need a computer, internet access, a web browser, and an email account. Popular wiki hosting sites include Wikispaces and PbWiki. The document provides examples of how wikis are used for class projects and communication at the secondary school level.