Does anyone have the specific definition of a "Group Health Plan" other than the standard "any plan offering health care to employees, etc..."?

Reason: I want to know if I should include our dental plan on our HIPAA notices. I'm assuming "yes" since a dental plan is an employer-provided health care plan. If anyone could confirm this, however, that'd be much appreciated.

HIPAA has some specific rules on the inclusion or exclusion of dental plans. See ERISA Section 706©. In my experience, most dental plans meet the requirements to be excluded from HIPAA.