A wiki is a website with content developed and added by a community of people. Wikipedia is perhaps the best-known example of a wiki.

Why Do You Need to Know About Wikis?

Wikis allow a number of people to collaborate on writing and editing information for the web. If one person has made a mistake in a document, others can revert the page back to its original state or correct the information. Wikis may be open for anyone on the internet to participate in, as is the case with Wikipedia. They may also be used internally in organizations as collaboration tools.

Wikipedia is the best known example of a wiki.