Mass. Gen. Laws ch. 271, § 51
(a) As used in this section, the following terms shall have the following meanings unless the context clearly requires otherwise:-
''First responder'', a law enforcement officer, a paid, call, reserve or volunteer firefighter, a paid, call, reserve or volunteer emergency medical technician or any other person whose usual and regular duties include rendering assistance at the scene of a crime, accident or other emergency.
''Immediate family member'', a spouse, child, step-child, adopted child, sibling, step sibling, adopted sibling, parent, step-parent, legal guardian, adoptive parent, grandparent or grandchild.