Wiki is Hierarchical Information compilation. It is article centric. Say a person A writes on a topic. person B can update it. The article itself can contain an Index for the Inner Items. Several Such articles can be linked together like you use tag cloud. By default Commenting on the article is not provided, you can do that with some twik in the script. They are best for Educational or Information Articles.

CMS allows Blogging, Articles, Books, Media sharing and everything. Each content is called a Node. Access control is allocated by administrator. So basically It is more interactive one with several Options.

Wiki is preferred for Tutorial Sites.