From the description:
Wiki provides a way for you to share your knowledge about a topic. Wikis are written and edited by groups of people. When you contribute to a Wiki you join a community of other people knowledgeable in the topic. Unlike reviews where each person's opinion appears separately, a Wiki is a single file that is edited by many people.
You can create Wikis about a many different things on Amazon. For example, you might create a Wiki to describe a particular opera recording. Within that Wiki you could create links to Wiki entries defining words such as "soprano" and "coloratura". (See instructions that follow.)
You can view how a particular Wiki entry has changed over time, to see who has contributed what and when, and you can subscribe to be notified by email of any future updates to Wikis you are interested in.
Think of a Wiki as an encyclopedia entry that everyone who comes to the page will read. You should put in relevant factual information that you believe will be of value to others who visit the page. A Wiki is not the place to express your opinion; that's what Customer Reviews and Customer Discussions are for. As always, please treat the Amazon community with respect by not writing inappropriate or off-topic comments.