If a user or a group is assigned the permission 'Default' for the object security, that user or group will have no access to that object as illustrated below:
From the above picture, none of the users from 'Everyone' group will have access to this object.
However, if 'Everyone' group has Full Control, View or Modify permissions in the object's parent folder and checks the "Apply Changes in permissions to all children objects" setting, then the user will be able to see the object.
