Definition of handwaving:
(adj) :
Pertaining to empty gesturing, with little substance behind it; vague; not supported by data.
(adj) :
(not comparable) Waving the hands.
(n) :
(chiefly figuratively) Alternative form of hand waving (“empty gesturing”). [(idiomatic) Discussion or argumentation involving approximation, vagueness, educated guessing, or the attempt to explain or excuse vagaries.]