linear descendents

For the purpose of this, ‘relative’ means : ‐
(a) spouse of the Individual;
(b) brother or sister of the individual;
(c) brother or sister of the spouse of the individual;
(d) brother or sister of the either of the parents of the individual;
(e) any lineal ascendant or descendant of the individual;
(f) any lineal ascendant or descendant of the spouse of the individual;
(g) spouse of the person referred to in clause (ii) to (vi).

check this link  also

/forum/relatives-u-s-56-2-vii-from-whom-gift-is-permissible--98674.asp