A wiki is collaborative tool for editing a single document. In instruction, wikis can be used for group writing assignments, or projects, or simply to allow multiple authors to craft a page. This page, https://cft.vanderbilt.edu/guides-sub-pages/wikis/, explains more about using wikis as an instructional tool for creating and evaluating. 

Canvas does not have a tool specifically called "wiki", however, each page is able to be edited by multiple authors when designated by the instructor. To create a wiki for your class, follow these instructions to create a new page in Canvas. Then, change the settings on the page to allow "anyone" to edit. One important feature to note is that the Canvas Pages tool does not track participation and contribution statistics like the Blackboard Wiki tool did, which may affect grading policies.

This guide from Northwestern University provides step-by-step instructions on pages 3 & 4 for creating and using wiki pages in Canvas: http://lmsblog.it.northwestern.edu/2014/12/02/student-blog-and-journal/