SP.Taxonomy.TermGroup.isSystemGroup property (sp.taxonomy)
Specifies information about whether this TermGroup object is the system TermGroup. The system TermGroup is the TermGroup where TermSet objects are used by the system itself.
Applies to: apps for SharePoint | SharePoint Foundation 2013 | SharePoint Server 2013
var value = SP.Taxonomy.TermGroup.get_isSystemGroup()