Section 2(1)(a) in The Border Security Force Act, 1968
(a)"active duty", in relation to a person subject to this Act, means any duty as a member of the Force during the period in which such person is attached to, or forms part of, a unit of the Force-(i)which is engaged in operations against an enemy, or(ii)which is operating at a picket or engaged on patrol or other guard duty along the borders of India,