The Collaborative International Dictionary of English v.0.48:

Ballooning \Bal*loon"ing\, n.
   1. The art or practice of managing balloons or voyaging in
      them; the sport of riding in balloons.

   Syn: balloonry (archaic)
        [1913 Webster +PJC]

   2. (Stock Exchange) The process of temporarily raising the
      value of a stock, as by fictitious sales. [U.S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

ballooning
    n 1: flying in a balloon