A wiki is a type of website that allows users to collaboratively edit its content. Wikis are commonly used for project management, operations manuals, event planning, FAQs, and knowledgebases where multiple people need to contribute and edit content together. There are self-hosted wiki software that can be installed locally, as well as hosted wiki services where the software is accessed online through a provider. Popular options for self-hosted wikis include MediaWiki and PhpWiki, while hosted services like PBwiki and SeedWiki allow wiki usage without software installation or maintenance.