The Google MapMaker is no longer in operation, having been decommissioned in 2017 to be replaced by Google Maps functionality. Preceding 2017, though, Google MapMaker was a tool that suggested edits to Google Maps by ordinary web users.
For instance, Google MapMaker might ask a web user if the location of a business was correct, the name was correct, or other data about the area visited by a web user was correct. Some of these queries may still be used by Google Maps, but they are no longer put forward by Google MapMaker.