A wiki is a 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 link 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 (See Fig. 1). To create a wiki for your class, follow this link for instructions on how 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.
Figure 1: Allow anyone to edit a Canvas page
This guide from Northwestern University provides step-by-step instructions on pages 3 and 4 for creating and using wiki pages in Canvas.
Canvas campus and vendor resources