Any user who can view the page but is not a workflow participant.
A non-workflow participant refers to any user who has view permissions for a page but not edit permissions and is not a reviewer in that page's workflow. This means that non-workflow participants are not able to view a page in a draft state (that is, a page undergoing a publishing workflow). Non-workflow participants will only be able to view the published version of the page, if one exists.
By contrast, any workflow participant may make edits to the page, though only reviewers may approve or return the workflow steps.