Reviews are a new functionality Thread Types Plus introduces for Article and Recipe threads. You can specifically disable it for either type under ACP > Setup > Options > [TH] Thread Types Plus: Reviews > Reviewable thread types.
When enabled, viewing a thread of the respective type will display a new tab bar that allows you to switch between posts and reviews. Reviewing a thread works the same way as reviewing a Resource in the XenForo Resource Manager, or Reviewing a Media/Album in the XenForo Media Gallery Official Plugins.
The Rate Article permission in the [TH] Thread types article permissions permission group allows you to control which of your users can create a new review. Thread authors with the Can reply to reviews for own articles can additionally reply once to each review.